input: touchscreen: fix buffer overflow issue in synaptics driver

Fix buffer overflow issue in synaptics touch driver while copying
the contents of "strptr" into "firmware_id". This code change is
meant to fix the same.

Change-Id: I8ea96af558eff540a37fb8e7da730c74502622aa
Signed-off-by: Shantanu Jain <shjain@codeaurora.org>