[SCSI] megaraid_sas: do not process cmds if hw_crit_error is set

Checks if hw_crit_error is set.
If it is set, we donot process commands.
Checks added in megasas_queue_command and command completion routines.

Signed-off-by: Sumant Patro <sumant.patro@lsi.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>