Input: rotary-encoder - defer calls gpio_to_irq()

Don't call gpio_to_irq() on GPIOs before gpio_request() succeeded on
them. This avoids Ooopses with incorrect DT bindings.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>