md: dm-req-crypt: Initialize auto variable

req_crypt_should_encrypt() and req_crypt_should_deccrypt() APIs are
using variable ret without initialization. This could cause these APIs
to return wrong values. Initialized ret with proper value.

Change-Id: I42ec8c12f02bf22b0434c3931842609cd9a8b8e0
Signed-off-by: Dinesh K Garg <dineshg@codeaurora.org>