input: synaptics_fw_update: Add force update entry

Add sysfs entry option to force update firmware, regardless
of versioning.

This patch is propagated from msm-3.4 kernel.
(commit: 5e0360e146dae56d085ed96c3ae62a9339fce1d5
input: synaptics_fw_update: Add force update entry)
Also cleared checkpatch warning on msm-3.18 kernel.

Change-Id: I85a12c531ee3d64a74da272b6e73b514eafc136a
Signed-off-by: Amy Maloche <amaloche@codeaurora.org>
Signed-off-by: Sudhakar Manapati <smanap@codeaurora.org>