input: touchscreen: fix issues found during static analysis

Prevent a NULL pointer dereference and a suspicious dereference
of a pointer before a NULL check. Also check the return value
of devm_kzalloc, to fix NULL pointer check related issues found
during static analysis.

Change-Id: I3ba87e2491c70752ecb9c43b7143c71ec3326f08
Signed-off-by: Himanshu Aggarwal <haggarwa@codeaurora.org>