Blackfin SPI Driver: add timeout while waiting for SPIF in dma irq handler

The "while" endless loop will cause the system hang if hardware error, so
we add timeout control to make the system alive.

Signed-off-by: Mike Frysinger <vapier.adi@gmail.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>