Clean up various C source and headers to appease -Wstrict-prototypes

In C, func() is a function taking an unspecified number of arguments,
vs func(void) a function taking no arguments. In C++ both forms indicate
"no arguments."

Update these headers to use the (void) form, which is correct in both
languages and avoids complaints when -Wstrict-prototypes is specified.

src/rp2_common/hardware_claim/include/hardware/claim.h

@@ -87,7 +87,7 @@ void hw_claim_clear(uint8_t *bits, uint bit_index);
  *
  * \return a token to pass to hw_claim_unlock()
  */
-uint32_t hw_claim_lock();
+uint32_t hw_claim_lock(void);
 
 /*! \brief Release the runtime mutual exclusion lock provided by the `hardware_claim` library
  *  \ingroup hardware_claim
@@ -98,4 +98,4 @@ uint32_t hw_claim_lock();
  */
 void hw_claim_unlock(uint32_t token);
 
-#endif
+#endif