firmware: imx: scu-irq: Free mailbox client on failure at imx_scu_enable_general_irq_...

firmware: imx: scu-irq: Free mailbox client on failure at imx_scu_enable_general_irq_channel()

The IRQ mailbox is an optional channel and does not need to be kept until
driver removal when an error occurs. Free the allocated memory in the
error path.

Add 'goto free_cl' when mbox_request_channel_byname() fails, to keep free
at one place.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>