drivers: misc: ti-st: fix debugfs creation error handling

In case the debugfs creation fails the whole init process was failing.
There is no need to do this as the shared transport can work without it.
Fix it so it just reports the failure and continue.

Signed-off-by: Eyal Reizer <eyalr@ti.com>
Signed-off-by: Gigi Joseph <gigi.joseph@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>