vfio/pds: fix return value in pds_vfio_get_lm_file()

anon_inode_getfile() never returns NULL pointer, it will return
ERR_PTR() when it fails, so replace the check with IS_ERR().

Fixes: bb500db ("vfio/pds: Add VFIO live migration support")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Brett Creeley <brett.creeley@amd.com>
Link: https://lore.kernel.org/r/20230819023716.3469037-1-yangyingliang@huawei.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

Author: Yang Yingliang

drivers/vfio/pci/pds/lm.c

@@ -31,7 +31,7 @@ pds_vfio_get_lm_file(const struct file_operations *fops, int flags, u64 size)
 	/* Create file */
 	lm_file->filep =
 		anon_inode_getfile("pds_vfio_lm", fops, lm_file, flags);
-	if (!lm_file->filep)
+	if (IS_ERR(lm_file->filep))
 		goto out_free_file;
 
 	stream_open(lm_file->filep->f_inode, lm_file->filep);