drivers/misc/ti-st: use cpu friendly completions

Be nice to CPU and don't hog the resources, use a nice wait_for_interruptible
timeout for completions instead of wait_for_timeout which is
non-interruptible.

Signed-off-by: Pavan Savoy <pavan_savoy@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>