dmaengine: ti: k3-psil: fix deadlock on error path

commit 172d59ec upstream.

The mutex_unlock() is missed on error path of psil_get_ep_config()
which causes deadlock.
Add missed mutex_unlock().

Fixes: 8c6bb62f ("dmaengine: ti: k3 PSI-L remote endpoint configuration")
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>