ipmi_watchdog: Fix read syscall not responding to signals during sleep

Read syscall cannot response to sigals when data_to_read remains at 0
and the while loop cannot break.  Check signal_pending in the loop.

Reported-by: Zhen Ni <zhen.ni@easystack.cn>
Message-Id: <20230517085412.367022-1-zhen.ni@easystack.cn>
Signed-off-by: Corey Minyard <minyard@acm.org>