input: synaptics_dsx_core: make clocks as optional for secure touch

Make clocks needed for secure touch as optional. Hence, even if the
clocks are not defined, just proceed further and initialise the secure
touch session.

Change-Id: Id8fb80ca0297bc1d1854fdc710abce6a4d2f9620
Signed-off-by: Abinaya P <abinayap@codeaurora.org>