mmc: host: omap_hsmmc: checking for NULL instead of IS_ERR()

devm_pinctrl_get() returns error pointers, it never returns NULL.

Fixes: 455e5cd6 ("mmc: omap_hsmmc: Pin remux workaround to support SDIO interrupt on AM335x")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>