input: touchscreen: gt9xx: fix memory corruption in Goodix driver

Fix memory corruption in Goodix touchscreen driver, by resetting
the global structure cmd_head to zero (except *data and wr flag)
in goodix_tool_write handler on error case.

Change-Id: I4f7f8f464b93571627b922b10c10a65826228e42
Signed-off-by: Vevek Venkatesan <vevekv@codeaurora.org>