staging: ccree: fold common code into function

Fold common code copying MAC to/from a temp. buffer
into an inline function instead of keeping multiple
open coded versions of same.

Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>