spi: bcm2835: Do not call gpiod_put() on invalid descriptor

If we are unable to lookup the chip-select GPIO, the error path will
call bcm2835_spi_cleanup() which unconditionally calls gpiod_put() on
the cs->gpio variable which we just determined was invalid.

Fixes: 21f252c ("spi: bcm2835: reduce the abuse of the GPIO API")
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://patch.msgid.link/20250401224238.2854256-1-florian.fainelli@broadcom.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-bcm2835.c

@@ -1162,7 +1162,8 @@ static void bcm2835_spi_cleanup(struct spi_device *spi)
 				 sizeof(u32),
 				 DMA_TO_DEVICE);
 
-	gpiod_put(bs->cs_gpio);
+	if (!IS_ERR(bs->cs_gpio))
+		gpiod_put(bs->cs_gpio);
 	spi_set_csgpiod(spi, 0, NULL);
 
 	kfree(target);