media: wl128x: Fix some error handling in fmc_prepare()

The st_register() returns have changed over time, but these days it
never returns -1.  We should just be checking for any negative error
codes.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/radio/wl128x/fmdrv_common.c

@@ -1524,7 +1524,7 @@ int fmc_prepare(struct fmdev *fmdev)
 		}
 
 		ret = 0;
-	} else if (ret == -1) {
+	} else if (ret < 0) {
 		fmerr("st_register failed %d\n", ret);
 		return -EAGAIN;
 	}