MIPS: dma-default: Fix 32-bit fall back to GFP_DMA
If there is a DMA zone (usually 24bit = 16MB I believe), but no DMA32
zone, as is the case for some 32-bit kernels, then massage_gfp_flags()
will cause DMA memory allocated for devices with a 32..63-bit
coherent_dma_mask to fall back to using __GFP_DMA, even though there may
only be 32-bits of physical address available anyway.
Correct that case to compare against a mask the size of phys_addr_t
instead of always using a 64-bit mask.