input: synaptics: add NULL pointer check

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

CRs-Fixed: 712847
Change-Id: I59ee5b00b124bc49fcc5d9d8bbfcb393fa70de05
Signed-off-by: Sarada Prasanna Garnayak <c_sgarna@codeaurora.org>