Input: mpr121 - switch to using managed resources

This change switches the driver to use devm_* managed resources APIs to
request the resources in probe to simplify probe error path and module
unloading and does away with remove function.

Signed-off-by: Pramod Gurav <pramod.gurav@smartplayin.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>