[ Upstream commit6b207ce8a9] dma_map_sg return 0 on error, fix the error check, and return -EIO to caller. Fixes:dbc049eee7("mailbox: Add driver for Broadcom FlexRM ring manager") Signed-off-by: Jack Wang <jinpu.wang@ionos.com> Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org> Signed-off-by: Sasha Levin <sashal@kernel.org>