[SCSI] qla4xxx: Use polling mode for disable interrupt mailbox completion

Disable Interrupt MBX completion will disable the interrupt on
successful completion.  Fixed the bug where driver was waiting for
Interrupt to come in for its completion.  Now driver will poll for
disable interrupt MBX completion.

Signed-off-by: Sarang Radke <sarang.radke@qlogic.com>
Signed-off-by: Vikas Chaudhary <vikas.chaudhary@qlogic.com>
Reviewed-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>