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_dma/include/hardware/dma.h

@@ -595,7 +595,7 @@ inline static void dma_sniffer_set_byte_swap_enabled(bool swap) {
  *  \ingroup hardware_dma
  *
  */
-inline static void dma_sniffer_disable() {
+inline static void dma_sniffer_disable(void) {
     dma_hw->sniff_ctrl = 0;
 }