iommu/amd: Fix NULL dereference bug in match_hid_uid

iommu/amd: Fix NULL dereference bug in match_hid_uid

BugLink: https://bugs.launchpad.net/bugs/1820990
Add a non-NULL check to fix potential NULL pointer dereference
Cleanup code to call function once.

Signed-off-by: Aaron Ma <aaron.ma@canonical.com>
Fixes: 2bf9a0a12749b ('iommu/amd: Add iommu support for ACPI HID devices')
Signed-off-by: Joerg Roedel <jroedel@suse.de>
(cherry picked from commit bb6bccba390c7d743c1e4427de4ef284c8cc6869)
Signed-off-by: Aaron Ma <aaron.ma@canonical.com>
Acked-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
Acked-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>