fix(bhi, leds): fixed faulty error handling due to always-false unsigned comparisons

-Wtype-limits revealed three errors in the firmware:

../pycardium/modules/sys_leds.c: In function 'mp_leds_get_rocket':
../pycardium/modules/sys_leds.c:207:10: warning: comparison is always false due to limited range of data type [-Wtype-limits]
  207 |  if (ret == -EINVAL) {
      |          ^~


../pycardium/mphalport.c: In function 'mp_hal_set_interrupt_char':
../pycardium/mphalport.c:115:8: warning: comparison is always true due to limited range of data type [-Wtype-limits]
  115 |  if (c != -1) {
      |        ^~

../epicardium/modules/bhi.c: In function 'epic_bhi160_enable_sensor':
../epicardium/modules/bhi.c:134:12: warning: comparison is always false due to limited range of data type [-Wtype-limits]
  134 |  if (vs_id < 0) {
      |            ^
../epicardium/modules/bhi.c: In function 'epic_bhi160_disable_sensor':
../epicardium/modules/bhi.c:191:12: warning: comparison is always false due to limited range of data type [-Wtype-limits]
  191 |  if (vs_id < 0) {
      |            ^

note, that on the target platform char and enums are unsigned. The compiler has probably removed all of these ifs so far because the conditions were determined to always be false.

epicardium/modules/bhi.c

@@ -131,7 +131,7 @@ int epic_bhi160_enable_sensor(
 	int result = 0;
 
 	bhy_virtual_sensor_t vs_id = bhi160_lookup_vs_id(sensor_type);
-	if (vs_id < 0) {
+	if (vs_id == (bhy_virtual_sensor_t)-1) {
 		return -ENODEV;
 	}
 
@@ -188,7 +188,7 @@ int epic_bhi160_disable_sensor(enum bhi160_sensor_type sensor_type)
 	int result = 0;
 
 	bhy_virtual_sensor_t vs_id = bhi160_lookup_vs_id(sensor_type);
-	if (vs_id < 0) {
+	if (vs_id == (bhy_virtual_sensor_t)-1) {
 		return -ENODEV;
 	}