net: mediatek: use dma_addr_t correctly

dma_alloc_coherent() expects a dma_addr_t pointer as its argument,
not an 'unsigned int', and gcc correctly warns about broken
code in the mtk_init_fq_dma function:

drivers/net/ethernet/mediatek/mtk_eth_soc.c: In function 'mtk_init_fq_dma':
drivers/net/ethernet/mediatek/mtk_eth_soc.c:463:13: error: passing argument 3 of 'dma_alloc_coherent' from incompatible pointer type [-Werror=incompatible-pointer-types]

This changes the type of the local variable to dma_addr_t.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>