Input: tnetv107x-keypad - don't treat NULL clk as an error

We should use IS_ERR() when checking whether clk_get() succeeded or
not since it returns errors by encoding error codes with ERR_PTR().

Signed-off-by: Jamie Iles <jamie@jamieiles.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>