Fix some of the (simpler) errors reported by the doxygen command (#617)

src/rp2_common/hardware_dma/include/hardware/dma.h

@@ -774,7 +774,7 @@ static inline void dma_timer_set_fraction(uint timer, uint16_t numerator, uint16
 /*! \brief Return the DREQ number for a given DMA timer
  *  \ingroup hardware_dma
  *
- * \param timer DMA timer number 0-3
+ * \param timer_num DMA timer number 0-3
  */
 static inline uint dma_get_timer_dreq(uint timer_num) {
     static_assert(DREQ_DMA_TIMER1 == DREQ_DMA_TIMER0 + 1, "");

src/rp2_common/hardware_exception/include/hardware/exception.h

@@ -16,7 +16,7 @@
  *
  * Methods for setting processor exception handlers
  *
- * Exceptions are identified by a \ref exception_num which is a number from -15 to -1; these are the numbers relative to
+ * Exceptions are identified by a \ref exception_number which is a number from -15 to -1; these are the numbers relative to
  * the index of the first IRQ vector in the vector table. (i.e. vector table index is exception_num plus 16)
  *
  * There is one set of exception handlers per core, so the exception handlers for each core as set by these methods are independent.
@@ -85,11 +85,11 @@ exception_handler_t exception_set_exclusive_handler(enum exception_number num, e
  * prior to the call to exception_set_exclusive_handler(), so that exception_set_exclusive_handler()
  * may be called again in the future.
  *
- * \param num Exception number \ref exception_nums
+ * \param num Exception number \ref exception_number
  * \param original_handler The original handler returned from \ref exception_set_exclusive_handler
  * \see exception_set_exclusive_handler()
  */
-void exception_restore_handler(enum exception_number, exception_handler_t original_handler);
+void exception_restore_handler(enum exception_number num, exception_handler_t original_handler);
 
 /*! \brief Get the current exception handler for the specified exception from the currently installed vector table
  * of the execution core

src/rp2_common/hardware_gpio/include/hardware/gpio.h

@@ -178,6 +178,12 @@ enum gpio_drive_strength {
  */
 void gpio_set_function(uint gpio, enum gpio_function fn);
 
+/*! \brief Determine current GPIO function
+ *  \ingroup hardware_gpio
+ *
+ * \param gpio GPIO number
+ * \return Which GPIO function is currently selected from list \ref gpio_function
+ */
 enum gpio_function gpio_get_function(uint gpio);
 
 /*! \brief Select up and down pulls on specific GPIO