Input: ad7879 - add check for read errors in interrupt

regmap_bulk_read() can return a non zero value on failure. The fix checks
if the function call succeeded before calling mod_timer. The issue was
identified by a static analysis tool.
Signed-off-by: Aditya Pakki <pakki001@umn.edu>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/touchscreen/ad7879.c

@@ -246,11 +246,14 @@ static void ad7879_timer(struct timer_list *t)
 static irqreturn_t ad7879_irq(int irq, void *handle)
 {
 	struct ad7879 *ts = handle;
+	int error;
 
-	regmap_bulk_read(ts->regmap, AD7879_REG_XPLUS,
+	error = regmap_bulk_read(ts->regmap, AD7879_REG_XPLUS,
 				 ts->conversion_data, AD7879_NR_SENSE);
-
-	if (!ad7879_report(ts))
+	if (error)
+		dev_err_ratelimited(ts->dev, "failed to read %#02x: %d\n",
+				    AD7879_REG_XPLUS, error);
+	else if (!ad7879_report(ts))
 		mod_timer(&ts->timer, jiffies + TS_PEN_UP_TIMEOUT);
 
 	return IRQ_HANDLED;