[SCSI] fusion: mptsas, increase discovery timout to 300 seconds

Increase the port enable timeout only for SAS from 30 to 300 seconds.
A customer request for the handling large topologies.

Signed-off-by: Eric Moore <Eric.Moore@lsil.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>