input: touchscreen: ft5x06: fix firmware force update issue

Force firmware update cannot work when touchscreen controller
cannot report correct family ID. If touchscreen is does not work
in correct state and it reports wrong family ID, it cannot be
recovered by force update, this change use family ID from device
tree instead of read from controller register to fix this issue.

Change-Id: I85d24bfc68a7777053c15f28a84027260c68cebd
Signed-off-by: Bingzhe Cai <bingzhec@codeaurora.org>