Fix "Fix DAC960 driver on machines which don't support 64-bit DMA"

sparc32:

drivers/block/DAC960.c: In function 'DAC960_V1_EnableMemoryMailboxInterface':
drivers/block/DAC960.c:1168: error: 'DMA_32BIT_MASK' undeclared (first use in this function)
drivers/block/DAC960.c:1168: error: (Each undeclared identifier is reported only

Cc: <dac@conglom-o.org>
Cc: <stable@kernel.org>
Cc: Alessandro Polverini <alex@nibbles.it>
Cc: Jeff Garzik <jeff@garzik.org>
Cc: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>