Input: synaptics-rmi4 - fix error handling in SPI transport driver

Instantiating the rmi4 SPI transport driver without an interrupt assigned
caused the driver to fail to load, but it does not clean up its transport
device registration. Result may be a crash at a later time, for example
when rebooting the system.

Fixes: 8d99758d ("Input: synaptics-rmi4 - add SPI transport driver")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>