firmware: imx-dsp: Fix an error handling path in imx_dsp_setup_channels()

[ Upstream commit e527adfb ]

If mbox_request_channel_byname() fails, the memory allocated a few lines
above still need to be freed before going to the error handling path.

Fixes: 04632698

 ("firmware: imx: Save channel name for further use")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Daniel Baluta <daniel.baluta@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>