md: Remove unnecessary check

Remove unnecessary if condition check, which is always false. Compile
with stringent warning option reports below error,

drivers/md/dm-req-crypt.c:926:5: warning: 'and' of mutually exclusive
equal-tests is always 0 [enabled by default]
error, forbidden warning: dm-req-crypt.c:926
make[4]: *** [drivers/md/dm-req-crypt.o] Error 1
make[3]: *** [drivers/md] Error 2

Change-Id: I604b7e682dd776a941589f0a54f3ee311b858115
Signed-off-by: AnilKumar Chimata <anilc@codeaurora.org>