scsi: megaraid_sas: memset IOC INIT frame using correct size

Commit b9637d14 ("scsi: megaraid_sas: Resize MFA frame used for IOC
INIT to 4k") increased the size of IOC INIT frame to 4k.  Need to use
updated size when memsetting init_frame.

Signed-off-by: Shivasharan S <shivasharan.srikanteshwara@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>