Fix the following sparse warning:

drivers/scsi/megaraid/megaraid_sas_fusion.c:180:1: warning: symbol
'megasas_enable_intr_fusion' was not declared. Should it be static?
drivers/scsi/megaraid/megaraid_sas_fusion.c:202:1: warning: symbol
'megasas_disable_intr_fusion' was not declared. Should it be static?
drivers/scsi/megaraid/megaraid_sas_fusion.c:4233:6: warning: symbol
'megasas_refire_mgmt_cmd' was not declared. Should it be static?

Link: https://lore.kernel.org/r/20200407092827.18074-4-yanaijie@huawei.comReported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>