ps2/avr: use the correct file name (#16316)

This was missed in https://github.com/qmk/qmk_firmware/pull/14895.

Thanks to fauxpark for spotting this.

builddefs/common_features.mk

@@ -707,7 +707,7 @@ endif
 ifeq ($(strip $(PS2_USE_BUSYWAIT)), yes)
     PS2_ENABLE := yes
     SRC += ps2_busywait.c
-    SRC += ps2_io_avr.c
+    SRC += ps2_io.c
     OPT_DEFS += -DPS2_USE_BUSYWAIT
 endif