remoteproc: k3: Correctly release some resources allocated in k3_rproc_request_mbox()

remoteproc: k3: Correctly release some resources allocated in k3_rproc_request_mbox()

If an error occurs after a successful k3_rproc_request_mbox() call,
mbox_free_channel() should be called to avoid a leak.

Such a call is missing in the error handling path of k3_dsp_rproc_probe().
It is also missing both in the error handling path of k3_m4_rproc_probe()
and in the (in-existent) corresponding remove function.

Switch to managed resources to avoid these leaks and simplify the code.
Remove the now unneeded mbox_free_channel().

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Beleswar Padhi <b-padhi@ti.com>
Tested-by: Beleswar Padhi <b-padhi@ti.com>
Link: https://lore.kernel.org/r/df853ede72e9972c464415990b196289680e6acb.1756065142.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>