MFC r305536: Fix channel initialization in FBS mode.

Due to reading initialized variable, FIS receive area was always allocated
as 256 bytes, suitable for command-based switching, instead of 4096 bytes,
required for FIS-based switching. This caused memory corruption in case of
MFC r305536: Fix channel initialization in FBS mode.

Due to reading initialized variable, FIS receive area was always allocated
as 256 bytes, suitable for command-based switching, instead of 4096 bytes,
required for FIS-based switching. This caused memory corruption in case of
port multipliers used on FBS-capable HBAs (Marvell).