[SCSI] qla2xxx: Correct 8GB iIDMA support.

Original implementation manipulated the FC_GS values for
port-speed.  Transition the codes to use the driver's own
internal representations as this makes for a reduction in
duplicate 'conversion' codes throughout the driver.

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