usb: musb: maintain three states for buffer mappings instead of two

If dma buffers are mapped by a higher layer, with a boolean musb_request.mapped
it is still possible to call dma_sync_single_for_device() from
musb_g_giveback(), even if txstate()/rxstate() has called unmap_dma_buffer()
before falling back to pio mode.

Moreover, check for musb_ep->dma is moved within map_dma_buffer() so where
applicable checks for it are removed. And where possible, checks for
is_dma_capable() are merged with buffer map state check.

Signed-off-by: Mian Yousaf Kaukab <mian.yousaf.kaukab@stericsson.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/musb/musb_gadget.h b/drivers/usb/musb/musb_gadget.h
index dec8dc0..a55354f 100644
--- a/drivers/usb/musb/musb_gadget.h
+++ b/drivers/usb/musb/musb_gadget.h
@@ -35,13 +35,19 @@
 #ifndef __MUSB_GADGET_H
 #define __MUSB_GADGET_H
 
+enum buffer_map_state {
+	UN_MAPPED = 0,
+	PRE_MAPPED,
+	MUSB_MAPPED
+};
+
 struct musb_request {
 	struct usb_request	request;
 	struct musb_ep		*ep;
 	struct musb		*musb;
 	u8 tx;			/* endpoint direction */
 	u8 epnum;
-	u8 mapped;
+	enum buffer_map_state map_state;
 };
 
 static inline struct musb_request *to_musb_request(struct usb_request *req)