md: dm-req-crypt: Fix compilation errors

During the kernel upgrade few functions are deprecated which
results in compilation errors on dm-req-crypt driver, this
patch fixes those compilation errors.

Change-Id: I8fadd8ca81e35292174199afd3c4508ecabf55b5
Signed-off-by: AnilKumar Chimata <anilc@codeaurora.org>