input: synaptics_dsx: fix up world writable sysfs file

Allowing the data sysfs file is not a good idea. We don't need this
sysfs file to be world writable or group writable. By default only
root should be able to write to this file. Change the write permissions
of this file to S_IWUSR (00200).

Signed-off-by: Himanshu Aggarwal <haggarwa@codeaurora.org>
Change-Id: I1d92d0e3eb2cfdc52a3873babe94c9c562a9df85