Input: mpr121 - set missing event capability

commit 9723ddc8fe0d76ce41fe0dc16afb241ec7d0a29d upstream.

This driver reports misc scan input events on the sensor's status
register changes.  But the event capability for them was not set in the
device initialization, so these events were ignored.

This change adds the missing event capability.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Oliver Neukum <ONeukum@suse.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Willy Tarreau <w@1wt.eu>