integrity: remove redundant initialization of variable ret

The variable ret is being initialized with a value that is never read
and it is being updated later with a new value.  The initialization is
redundant and can be removed.

Fixes: eb5798f2 ("integrity: convert digsig to akcipher api")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: James Morris <jamorris@linux.microsoft.com>
Addresses-Coverity: ("Unused value")
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>