input: touchscreen: bu21150: change IRQ to edge trigger

The AFE is programmed to be edge trigger. Set IRQ flag to edge trigger
in driver to match with HW.

Change-Id: I70c96895e7bc698cb167c3e9f051169966f0f1be
Signed-off-by: Jing Lin <jinglin@codeaurora.org>
Signed-off-by: Bharat Pawar <bpawar@codeaurora.org>