media: radio-wl1273: fix return code for the polling routine

All poll handlers should return a poll flag, and not error codes. So,
instead of returning an error, do the right thing here,
e. g. to return EPOLERR on errors, just like the V4L2 VB2 code.

Solves the following sparse warning:
    drivers/media/radio/radio-wl1273.c:1099:24: warning: incorrect type in return expression (different base types)
    drivers/media/radio/radio-wl1273.c:1099:24:    expected restricted __poll_t
    drivers/media/radio/radio-wl1273.c:1099:24:    got int

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/radio/radio-wl1273.c

@@ -1096,7 +1096,7 @@ static __poll_t wl1273_fm_fops_poll(struct file *file,
 	struct wl1273_core *core = radio->core;
 
 	if (radio->owner && radio->owner != file)
-		return -EBUSY;
+		return EPOLLERR;
 
 	radio->owner = file;