scsi: megaraid_sas: clean function declarations in megaraid_sas_base.c up

We get a few warnings when building kernel with W=1:
drivers/scsi/megaraid/megaraid_sas_fusion.c:281:1: warning: no previous prototype for 'megasas_free_cmds_fusion' [-Wmissing-prototypes]
drivers/scsi/megaraid/megaraid_sas_fusion.c:714:1: warning: no previous prototype for 'megasas_ioc_init_fusion' [-Wmissing-prototypes]
....

In fact, these functions are declared in
drivers/scsi/megaraid/megaraid_sas_base.c, but should be declared in a
header file, thus can be recognized in other file.

So this patch adds the declarations into
drivers/scsi/megaraid/megaraid_sas_fusion.h.

Signed-off-by: Baoyou Xie <baoyou.xie@linaro.org>
Acked-by: Sumit Saxena <sumit.saxena@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>