ipmi: msghandler: Make symbol 'remove_work_wq' static

The sparse tool complains as follows:

drivers/char/ipmi/ipmi_msghandler.c:194:25: warning:
 symbol 'remove_work_wq' was not declared. Should it be static?

This symbol is not used outside of ipmi_msghandler.c, so
marks it static.

Fixes: 1d49eb91

 ("ipmi: Move remove_work to dedicated workqueue")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Message-Id: <20211123083618.2366808-1-weiyongjun1@huawei.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>