ARM: shmobile: ap4evb: Simplify tsc2007 pen state read function

The pen state is retrieved by reading the state of a pin used as an IRQ.
There's no need to reconfigure the pin as a pure GPIO, as the IRQ pin
state can be read.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>