Explicitly use empty initializer list

Per C and CPP spec, {} will set all elements to their "static" defined
equivalents (i.e. 0).

src/rp2_common/hardware_pio/include/hardware/pio.h

@@ -647,10 +647,9 @@ static inline void sm_config_set_mov_status(pio_sm_config *c, enum pio_mov_statu
  * \return the default state machine configuration which can then be modified.
  */
 static inline pio_sm_config pio_get_default_sm_config(void) {
- #if PICO_PIO_USE_GPIO_BASE
-    pio_sm_config c = {0, 0, 0, 0, -1};
-#else
-    pio_sm_config c = {0, 0, 0, 0};
+    pio_sm_config c = {};
+#if PICO_PIO_USE_GPIO_BASE
+    c.pinhi = -1;
 #endif
     sm_config_set_clkdiv_int_frac(&c, 1, 0);
     sm_config_set_wrap(&c, 0, 31);