crypto: qat/qat_6xxx - Fix NULL vs IS_ERR() check in adf_probe()

The pcim_iomap_region() returns error pointers.  It doesn't return NULL
pointers.  Update the check to match.

Fixes: 17fd7514 ("crypto: qat - add qat_6xxx driver")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Acked-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>