ARM: dts: stm32: use the correct clock source for CEC on stm32mp151

stable inclusion
from stable-v5.10.132
commit 35ce2c64e57e51be166f575330968b6b31298d6d
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5YS3T

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=35ce2c64e57e51be166f575330968b6b31298d6d



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[ Upstream commit 78ece8cc ]

The peripheral clock of CEC is not LSE but CEC.

Signed-off-by: Gabriel Fernandez <gabriel.fernandez@foss.st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>