staging: fbtft: Fix error path in fbtft_driver_module_init()

If registering the platform driver fails, the function must not return
without undoing the spi driver registration first.

Fixes: c296d5f9

 ("staging: fbtft: core support")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20220118181338.207943-1-u.kleine-koenig@pengutronix.de


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>