usb: Allow up to 7 storage devices

The current limit of 5 is not enough for the driver model USB tests. Really
we should not have a limit but the driver model code still uses the
usb_dev_desc[] array, which has a limit.

Increasing the limit by 2 should not bother anyone. Adjust it.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Marek Vasut <marex@denx.de>
diff --git a/common/usb_storage.c b/common/usb_storage.c
index 4fa6538..e61a8c8 100644
--- a/common/usb_storage.c
+++ b/common/usb_storage.c
@@ -65,7 +65,7 @@
 static ccb usb_ccb __attribute__((aligned(ARCH_DMA_MINALIGN)));
 static __u32 CBWTag;
 
-#define USB_MAX_STOR_DEV 5
+#define USB_MAX_STOR_DEV 7
 static int usb_max_devs; /* number of highest available usb device */
 
 static block_dev_desc_t usb_dev_desc[USB_MAX_STOR_DEV];