spi: bcm2835: Release the DMA channel if probe fails after dma_init

The DMA channel was not released if either devm_request_irq() or
devm_spi_register_controller() failed.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reviewed-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Link: https://lore.kernel.org/r/20191212135550.4634-3-peter.ujfalusi@ti.com
Signed-off-by: Mark Brown <broonie@kernel.org>