Input: tps6507x-ts - simplify function return logic

The invoked function already returns zero on success or a negative
errno code so there is no need to open code the logic in the caller.

This also fixes the following make coccicheck warning:

drivers/input/touchscreen/tps6507x-ts.c:57:5-8: WARNING: end returns can be simplified

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>