scsi: ibmvscsi: Make some functions static

Fix the following warning:

drivers/scsi/ibmvscsi/ibmvscsi.c:2387:12: warning: symbol
'ibmvscsi_module_init' was not declared. Should it be static?
drivers/scsi/ibmvscsi/ibmvscsi.c:2409:13: warning: symbol
'ibmvscsi_module_exit' was not declared. Should it be static?

Link: https://lore.kernel.org/r/20200520091036.247286-1-chentao107@huawei.com
Signed-off-by: Chen Tao <chentao107@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>