Input: atmel_mxt_ts - fix a few issues reported by Coverity

This should fix the following issues reported by Coverity:

*** CID 1230625:  Logically dead code  (DEADCODE)
/drivers/input/touchscreen/atmel_mxt_ts.c: 1692 in mxt_initialize()

*** CID 12306276:  Missing break in switch  (MISSING_BREAK)
/drivers/input/touchscreen/atmel_mxt_ts.c: 1436 in mxt_get_object_table()

*** CID 1230629:  Out-of-bounds write  (OVERRUN)
/drivers/input/touchscreen/atmel_mxt_ts.c: 1267 in mxt_update_cfg()

*** CID 1230632:  Unused pointer value  (UNUSED_VALUE)
/drivers/input/touchscreen/atmel_mxt_ts.c: 1211 in mxt_update_cfg()

Acked-by: Nick Dyer <nick.dyer@itdev.co.uk>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>