msm: mink: Accept zero args for invoke command

Currently, INVOKE IOCTL assumes presence of atleast one arg. This
assumption is not correct. Hence, adding support for zero args in
INVOKE IOCTL.

Change-Id: Ib44789559c69e5808ed362cf9191486c93b2b66e
Signed-off-by: Dinesh K Garg <dineshg@codeaurora.org>