Input: sentelic - fix error return when fsp_reg_write fails

Currently when the call to fsp_reg_write fails -EIO is not being returned
because the count is being returned instead of the return value in retval.
Fix this by returning the value in retval instead of count.

Addresses-Coverity: ("Unused value")
Fixes: fc69f4a ("Input: add new driver for Sentelic Finger Sensing Pad")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20200603141218.131663-1-colin.king@canonical.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/mouse/sentelic.c

@@ -441,7 +441,7 @@ static ssize_t fsp_attr_set_setreg(struct psmouse *psmouse, void *data,
 
 	fsp_reg_write_enable(psmouse, false);
 
-	return count;
+	return retval;
 }
 
 PSMOUSE_DEFINE_WO_ATTR(setreg, S_IWUSR, NULL, fsp_attr_set_setreg);