firmware/imx-dsp: Fix use_after_free in imx_dsp_setup_channels()

dsp_chan->name and chan_name points to same block of memory,
because dev_err still needs to be used it,so we need free
it's memory after use to avoid use_after_free.

Fixes: e527adfb ("firmware: imx-dsp: Fix an error handling path in imx_dsp_setup_channels()")
Signed-off-by: Hao Ge <gehao@kylinos.cn>
Reviewed-by: Daniel Baluta <daniel.baluta@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>