MIPS: mm: remove mips_dma_mapping_error

dma_mapping_error() already checks if ops->mapping_error is a null
pointer

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17881/


Signed-off-by: James Hogan <jhogan@kernel.org>