input: synaptics_dsx: remove vkey kobject in remove

Remove virtual key kobject in module remove only if vkeys
are supported.

CRs-fixed: 741470
Change-Id: I11460172a4c2dce99e4fd37f2aaf5b0d643f837c
Signed-off-by: Mohan Pallaka <mpallaka@codeaurora.org>