mtd: blackfin NFC: fix hang when using NAND on BF527-EZKITs

The DMAs have different bit sizes on BF52x and BF54x.  From the PHRM:

"The 16-bit DMA Access Bus (DAB) connects the DMA controller to the
on-chip peripherals, PPI, SPI, Ethernet MAC, the SPORTs, NFC,
HOSTDP and the UARTs."

32-bit DMA won't work for BF52x.

Signed-off-by: Cliff Cai <cliff.cai@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>