[Bug] Fix missing variable for Backlight Breathing (#15199)

* [Bug] Fix missing varaible for Backlight Breathing

* Better fix

* formatting

quantum/backlight/backlight_avr.c

@@ -331,9 +331,9 @@ bool is_breathing(void) { return !!(TIMSKx & _BV(TOIEx)); }
         do {                       \
             breathing_counter = 0; \
         } while (0)
-#    define breathing_max()                                                     \
-        do {                                                                    \
-            breathing_counter = breathing_period * breathing_ISR_frequency / 2; \
+#    define breathing_max()                                                           \
+        do {                                                                          \
+            breathing_counter = get_breathing_period() * breathing_ISR_frequency / 2; \
         } while (0)
 
 void breathing_enable(void) {
@@ -390,9 +390,9 @@ ISR(TIMERx_OVF_vect)
     } else {
         return;
     }
-    uint16_t interval = (uint16_t)breathing_period * breathing_ISR_frequency / BREATHING_STEPS;
+    uint16_t interval = (uint16_t)get_breathing_period() * breathing_ISR_frequency / BREATHING_STEPS;
     // resetting after one period to prevent ugly reset at overflow.
-    breathing_counter = (breathing_counter + 1) % (breathing_period * breathing_ISR_frequency);
+    breathing_counter = (breathing_counter + 1) % (get_breathing_period() * breathing_ISR_frequency);
     uint8_t index     = breathing_counter / interval % BREATHING_STEPS;
 
     if (((breathing_halt == BREATHING_HALT_ON) && (index == BREATHING_STEPS / 2)) || ((breathing_halt == BREATHING_HALT_OFF) && (index == BREATHING_STEPS - 1))) {
@@ -454,4 +454,4 @@ void backlight_init_ports(void) {
         breathing_enable();
     }
 #endif
-}
+}