input: ft5x06_ts: add NULL pointer check

Add null pointer exception check for pointers which
may be NULL after memory allocation failure and may
be deferenced.

Change-Id: Ied34d548bff27f8f6da9f4c81896e4505cdce218
Signed-off-by: Sarada Prasanna Garnayak <c_sgarna@codeaurora.org>