mmc: renesas_sdhi_internal_dmac: Fix missing unmap in error patch

This patch fixes an issue that lacks the dma_unmap_sg() calling in
the error patch of renesas_sdhi_internal_dmac_start_dma().

Fixes: 0cbc94da ("mmc: renesas_sdhi_internal_dmac: limit DMA RX for old SoCs")
Cc: <stable@vger.kernel.org> # v4.17+
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>