ipmi: ssif_bmc: Use EPOLLIN instead of POLLIN

This fixes the following sparse warning:
sparse warnings: (new ones prefixed by >>)
>> drivers/char/ipmi/ssif_bmc.c:254:22: sparse: sparse: invalid assignment: |=
>> drivers/char/ipmi/ssif_bmc.c:254:22: sparse:    left side has type restricted __poll_t
>> drivers/char/ipmi/ssif_bmc.c:254:22: sparse:    right side has type int

Fixes: dd2bc5cc ("ipmi: ssif_bmc: Add SSIF BMC driver")
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/all/202210181103.ontD9tRT-lkp@intel.com/


Signed-off-by: Quan Nguyen <quan@os.amperecomputing.com>
Message-Id: <20221024075956.3312552-1-quan@os.amperecomputing.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>