ata: pata_imx: fix devm_ioremap_resource() return value checking

devm_ioremap_resource() returns a pointer to the remapped memory or
an ERR_PTR() encoded error code on failure.  Fix the check inside
pata_imx_probe() accordingly.

Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Tejun Heo <tj@kernel.org>