bcopyxx/memmove: fix alignment logic for reverse moves

bcopyxx/memmove: fix alignment logic for reverse moves

The alignment logic for reverse moves is reversed, because the initial
edi, and therefore edx, points to the last byte, not to one byte
beyond the end.  Therefore, in the fully aligned case it will end in
11 binary, not in 00 binary as for the forward case.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>