input: synaptics_dsx: remove array declaration in write function

Remove array declaration in i2c write function of Synaptics DSX
touch driver and use the malloc function to allocate the memory.
This change is added to use heap memory instead of stack memory.

CRs-Fixed: 1010986
Change-Id: I8f2f75744bb442191d7d4577795d986e10ea1cf6
Signed-off-by: Shantanu Jain <shjain@codeaurora.org>