input: bu21150: fix unbalanced irq calls

In device open function, the client's irq is requested. In device release
function, the same irq is disabled. The calls are not balanced and cause
error when the device is re-opened. Fix it by changing disable_irq to
free_irq.

Change-Id: I9134837561e6fde369358c7b36e8b23a189ec8f2
Signed-off-by: Jing Lin <jinglin@codeaurora.org>