crypto: caam - fix caam_jr_alloc() ret code

caam_jr_alloc() used to return NULL if a JR device could not be
allocated for a session. In turn, every user of this function used
IS_ERR() function to verify if anything went wrong, which does NOT look
for NULL values. This made the kernel crash if the sanity check failed,
because the driver continued to think it had allocated a valid JR dev
instance to the session and at some point it tries to do a caam_jr_free()
on a NULL JR dev pointer.
This patch is a fix for this issue.

Cc: <stable@vger.kernel.org>
Signed-off-by: Catalin Vasile <cata.vasile@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>