crypto: qat - Fix return value check in adf_chr_drv_create()

In case of error, the function device_create() returns ERR_PTR()
and never returns NULL. The NULL test in the return value check
should be replaced with IS_ERR().

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>