dma-mapping: reduce dma_mapping_error inline bloat

Thanks to the nested inlining, all drivers correctly calling
dma_mapping_error() after a mapping a page or single buffer generate two
calls to get_arch_dma_ops() per callsite, which all adds up to a fair
old chunk of useless code, e.g. ~3KB for an arm64 defconfig plus extras:

   text	   data	    bss	    dec	    hex	filename
13051391	1503898	 327768	14883057	 e318f1	vmlinux.o.old
13050751	1503898	 327768	14882417	 e31671	vmlinux.o.new

Give the compiler a hand by making it clear we want the same ops.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>