api: Fix building with CONFIG_API

This patch fixes building with CONFIG_API and CONFIG_USB_STORAGE.

USB_MAX_STOR_DEV is defined in include/usb.h, but
needed in api/api_storage.c.

Signed-off-by: Matthias Fuchs <matthias.fuchs@esd-electronics.com>

api/api_storage.c

@@ -30,6 +30,10 @@
 #include <common.h>
 #include <api_public.h>
 
+#if defined(CONFIG_CMD_USB) && defined(CONFIG_USB_STORAGE)
+#include <usb.h>
+#endif
+
 #define DEBUG
 #undef DEBUG