kasan: fix panic bug in check_channel_mask function

kasan: fix panic bug in check_channel_mask function

PD#172700

When open kasan, kernel paniced on P321:

Internal error: Oops: 96000005 [#1] PREEMPT SMP
PC is at strncmp+0x1e0/0x210
LR is at check_channel_mask+0x30/0xa8

[<ffffff900963ad10>] strncmp+0x1e0/0x210
[<ffffff9009e64418>] parse_speaker_channel_mask.isra.1+0x120/0x258
[<ffffff9009e6610c>] txl_chipset_init+0x8c/0xc0
[<ffffff9009e653ac>] aml_init_work_func+0x54/0x210
[<ffffff90090dcb18>] process_one_work+0x378/0x880
[<ffffff90090dd0bc>] worker_thread+0x9c/0x7a0
[<ffffff90090e6514>] kthread+0x184/0x1a0
[<ffffff9009083e80>] ret_from_fork+0x10/0x50

return value of of_property_read_string must be checked!

Change-Id: Ic0e0dcd0a3aa2f4ed10335e417f7db259a51fc95
Signed-off-by: tao zeng <tao.zeng@amlogic.com>