firewire: sbp2: remove redundant check for bidi command

[Bart van Asche:]  SCSI core never sets cmd->sc_data_direction to
DMA_BIDIRECTIONAL; scsi_bidi_cmnd(cmd) should be used instead to
test for a bidirectional command.

[Christoph Hellwig:]  Bidirectional commands won't ever be queued
anyway, unless a LLD or transport driver sets QUEUE_FLAG_BIDI.

So, simply remove the respective queuecommand check in the SBP-2
transport driver.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>