crypto: omap-sham - Remove useless check for non-null request

ahash_request 'req' argument passed by the caller
omap_sham_handle_queue() cannot be NULL here because it is obtained from
non-NULL pointer via container_of().

This fixes smatch warning:
    drivers/crypto/omap-sham.c:812 omap_sham_prepare_request() warn: variable dereferenced before check 'req' (see line 805)

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>