can: CAN_GRCAN should depend on HAS_DMA

If NO_DMA=y:

    drivers/built-in.o: In function `grcan_free_dma_buffers':
    grcan.c:(.text+0x2d7716): undefined reference to `dma_free_coherent'
    drivers/built-in.o: In function `grcan_allocate_dma_buffers':
    grcan.c:(.text+0x2d779c): undefined reference to `dma_alloc_coherent'

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: David S. Miller <davem@davemloft.net>