soc: qcom: geni: Provide parameter error checking

When booting with ACPI, the Geni Serial Engine is not set as the I2C/SPI
parent and thus, the wrapper (parent device) is unassigned.  This causes
the kernel to crash with a null dereference error.

Link: https://lore.kernel.org/r/20190905082555.15020-1-lee.jones@linaro.org
Fixes: 8bc529b2 ("soc: qcom: geni: Add support for ACPI")
Acked-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

drivers/soc/qcom/qcom-geni-se.c

@@ -630,6 +630,9 @@ int geni_se_tx_dma_prep(struct geni_se *se, void *buf, size_t len,
 	struct geni_wrapper *wrapper = se->wrapper;
 	u32 val;
 
+	if (!wrapper)
+		return -EINVAL;
+
 	*iova = dma_map_single(wrapper->dev, buf, len, DMA_TO_DEVICE);
 	if (dma_mapping_error(wrapper->dev, *iova))
 		return -EIO;
@@ -663,6 +666,9 @@ int geni_se_rx_dma_prep(struct geni_se *se, void *buf, size_t len,
 	struct geni_wrapper *wrapper = se->wrapper;
 	u32 val;
 
+	if (!wrapper)
+		return -EINVAL;
+
 	*iova = dma_map_single(wrapper->dev, buf, len, DMA_FROM_DEVICE);
 	if (dma_mapping_error(wrapper->dev, *iova))
 		return -EIO;