Input: max8997_haptic - add error handling for regulator and pwm

Let's start checking return value of regulator_enable and pwm_enable to
avoid errors. Fixes the following warning:

drivers/input/misc/max8997_haptic.c:185:19: warning: ignoring return value of ‘regulator_enable’, declared with attribute warn_unused_result [-Wunused-result]

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>