Fix Dynamic Macro Compilation for avr-gcc 5.4.0 + Linux (#21653)

Co-authored-by: Joel Challis <git@zvecr.com>

quantum/process_keycode/process_dynamic_macro.c

@@ -196,7 +196,7 @@ static keyrecord_t *macro_end = macro_buffer;
 static keyrecord_t *const r_macro_buffer = macro_buffer + DYNAMIC_MACRO_SIZE - 1;
 
 /* Like macro_end but for the second macro. */
-static keyrecord_t *r_macro_end = r_macro_buffer;
+static keyrecord_t *r_macro_end = macro_buffer + DYNAMIC_MACRO_SIZE - 1;
 
 /* A persistent pointer to the current macro position (iterator)
  * used during the recording. */