media: s5p_cec: limit msg.len to CEC_MAX_MSG_SIZE

stable inclusion
from stable-v5.10.154
commit 1609231f86760c1f6a429de7913dd795b9faa08c
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I64YCB

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1609231f86760c1f6a429de7913dd795b9faa08c



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[ Upstream commit 93f65ce0 ]

I expect that the hardware will have limited this to 16, but just in
case it hasn't, check for this corner case.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Lipeng Sang <sanglipeng1@jd.com>