crypto: omap-aes-gcm - deal with memory allocation failure

The OMAP gcm(aes) driver invokes omap_crypto_align_sg() without
dealing with the errors it may return, resulting in a crash if
the routine fails in a __get_free_pages(GFP_ATOMIC) call. So
bail and return the error rather than limping on if one occurs.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Tero Kristo <t-kristo@ti.com>
Tested-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>