Fix for return value from HID mod functions.

src/hid.c

@@ -9,7 +9,8 @@ static struct zmk_hid_report report = {
     {                                        \
         return -EINVAL;                      \
     }                                        \
-    WRITE_BIT(report.modifiers, mod, state);
+    WRITE_BIT(report.modifiers, mod, state); \
+    return 0;
 
 int zmk_hid_register_mod(zmk_mod modifier)
 {