BugLink: http://bugs.launchpad.net/bugs/1655969

commit 24c790fb upstream.

We should set "ret" to -EINVAL if iommu_group_get() fails.

Fixes: 55c99a4d ("iommu/amd: Use iommu_attach_group()")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>