[SCSI] megaraid: replace yield() with cond_resched()

For this driver cond_resched() seems to be a better alternative

Signed-off-by: Amol Lad <amol@verismonetworks.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>