iommu/pamu: Use kzfree() in fsl_pamu_probe()

Use kzfree() instead of opencoded memset with 0 followed by kfree().
Null check is not required since kzfree() checks for NULL internally.

Signed-off-by: Denis Efremov <efremov@linux.com>
Link: https://lore.kernel.org/r/20200604123709.96561-1-efremov@linux.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>