[Fix] lib8tion: enable fixed scale8 and blend functions (#25272)

lib8tion: enable fixed scale8 and blend functions

These FastLED derived lib8tion functions have been fixed and enabled by
default in FastLED. QMK just never set these defines, there is no reason
to keep the buggy implementation. It is assumed that nobody relied on
the buggy behavior.

builddefs/common_features.mk

@@ -722,6 +722,7 @@ ifeq ($(strip $(LIB8TION_ENABLE)), yes)
         # ATmegaxxU2 does not have hardware MUL instruction - lib8tion must be told to use software multiplication routines
         OPT_DEFS += -DLIB8_ATTINY
     endif
+    OPT_DEFS += -DFASTLED_SCALE8_FIXED=1 -DFASTLED_BLEND_FIXED=1
     SRC += $(LIB_PATH)/lib8tion/lib8tion.c
 endif