sdei_watchdog: Avoid exception during sdei handler

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I82QPR



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On Kunpeng920 platform, when firmware triggers SDEI event too soon,
A WARN_ON() will be called in sdei_watchdog_callback(), this leads
to warning "sdei: unsafe: exception during handler" being reported
in _sdei_handler().

As the comments for the warning mentioned,
We took a synchronous exception from the SDEI handler.
This could deadlock, and if you interrupt KVM it will
hyp-panic instead.

Remove the WARN_ON() to avoid potential issue and warning.

Fixes: 0fa83fd0 ("sdei_watchdog: avoid possible false hardlockup")
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>