usb: ehci: do not invalidate a NULL buffer

Its a valid use case to call ehci_submit_async() with a NULL buffer
with length 0. E.g. from usb_set_configuration().

As invalidate_dcache_range() isn't able to judge if the address
NULL is valid or not (depending on the SoC hardware configuration it
might be valid) do the check in ehci_submit_async() as here we know
that we don't have to invalidate such a buffer.

Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>

drivers/usb/host/ehci-hcd.c

@@ -592,8 +592,9 @@ ehci_submit_async(struct usb_device *dev, unsigned long pipe, void *buffer,
 	 * dangerous operation, it's responsibility of the calling
 	 * code to make sure enough space is reserved.
 	 */
-	invalidate_dcache_range((unsigned long)buffer,
-		ALIGN((unsigned long)buffer + length, ARCH_DMA_MINALIGN));
+	if (buffer != NULL && length > 0)
+		invalidate_dcache_range((unsigned long)buffer,
+			ALIGN((unsigned long)buffer + length, ARCH_DMA_MINALIGN));
 
 	/* Check that the TD processing happened */
 	if (QT_TOKEN_GET_STATUS(token) & QT_TOKEN_STATUS_ACTIVE)