ipmi: Don't call receive handler in the panic context

Received handlers defined as ipmi_recv_hndl member of struct
ipmi_user_hndl can take a spinlock.  This means that if the kernel
panics while holding the lock, a deadlock may happen on the lock
while flushing queued messages in the panic context.

Calling the receive handler doesn't make much meanings in the panic
context, simply skip it to avoid possible deadlocks.

Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>