codec_mm: config: fixed config error crash bug.

codec_mm: config: fixed config error crash bug.

PD#166937:
	not return errors when not find config.
	will crashed on:
[    9.478046@0] task: ffffffc05aea8d80 task.stack: ffffffc05a498000
[    9.484090@0] PC is at configs_config2str+0x2c/0x240
[    9.489001@0] LR is at configs_get_node_path_str+0x78/0xd4
[    9.494433@0] pc : [<ffffff800982f8cc>] lr : [<ffffff80098311c8>]
	pstate: 20000145
[    9.501935@0] sp : ffffffc05a49baf0
[    9.505386@0] x29: ffffffc05a49baf0 x28: ffffffc05a498000

Change-Id: Ia5985d3e5aa7aefecb6867e3d2ab29efc7592b9b
Signed-off-by: Zhi Zhou <zhi.zhou@amlogic.com>