rt2x00: RT2X00 should depend on HAS_DMA

If NO_DMA=y:

drivers/built-in.o: In function `rt2x00queue_unmap_skb':
drivers/net/wireless/rt2x00/rt2x00queue.c:129: undefined reference to `dma_unmap_single'
drivers/net/wireless/rt2x00/rt2x00queue.c:133: undefined reference to `dma_unmap_single'
drivers/built-in.o: In function `rt2x00queue_map_txskb':
drivers/net/wireless/rt2x00/rt2x00queue.c:112: undefined reference to `dma_map_single'
drivers/net/wireless/rt2x00/rt2x00queue.c:115: undefined reference to `dma_mapping_error'
drivers/built-in.o: In function `rt2x00queue_alloc_rxskb':
drivers/net/wireless/rt2x00/rt2x00queue.c:93: undefined reference to `dma_map_single'
drivers/net/wireless/rt2x00/rt2x00queue.c:95: undefined reference to `dma_mapping_error'

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: linux-wireless@vger.kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>