Fix bit numbers in comment for the example input reading routine (#119)

It looks like maybe the comment was copied from the one above for
reading the buttons. If so, the order of the parts were swapped but not
the bit numbers.

Author: bpeel

unbricked/input/main.asm

@@ -130,7 +130,7 @@ UpdateKeys:
   ; Poll the other half
   ld a, P1F_GET_DPAD
   call .onenibble
-  swap a ; A3-0 = unpressed directions; A7-4 = 1
+  swap a ; A7-4 = unpressed directions; A3-0 = 1
   xor a, b ; A = pressed buttons + directions
   ld b, a ; B = pressed buttons + directions