starfire: Fix dma_addr_t size test for MIPS

Commit 56543af9 "starfire: use BUILD_BUG_ON for netdrv_addr_t" revealed
that the preprocessor condition used to find the size of dma_addr_t
yielded the wrong result for some architectures and configurations.
This was kluged for 64-bit PowerPC in commit 3e502e63

 by adding yet
another case to the condition.  However, 64-bit MIPS configurations
are not detected reliably either.

This should be fixed by using CONFIG_ARCH_DMA_ADDR_T_64BIT, but that
isn't yet defined everywhere it should be.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>