[SCSI] qla2xxx: Don't hardcode fw_transfer_size for ISP2[45]xx parts.

Use the full buffer size available, as there's no reason to limit
the firwmare-image load-segment size for these parts.

Signed-off-by: Andrew Vasquez <andrew.vasquez@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>