firmware: raspberrypi: Fix devm_rpi_firmware_get documentation

The function documentation for devm_rpi_firmware_get() was missing
a description for the dev parameter.

Provide it and clear the warning produced here.

Fixes: f663204c ("firmware: raspberrypi: Introduce devm_rpi_firmware_get()")
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Link: https://lore.kernel.org/r/20230925151812.142480-1-kieran.bingham+renesas@ideasonboard.comSigned-off-by: Florian Fainelli <florian.fainelli@broadcom.com>

drivers/firmware/raspberrypi.c

@@ -378,6 +378,7 @@ EXPORT_SYMBOL_GPL(rpi_firmware_get);
 
 /**
  * devm_rpi_firmware_get - Get pointer to rpi_firmware structure.
+ * @dev:              The firmware device structure
  * @firmware_node:    Pointer to the firmware Device Tree node.
  *
  * Returns NULL is the firmware device is not ready.