usb: musb: gadget: DBG() already prints function name

In the gadget code, there are several DBG() macro invocations that explicitly
print the calling function's name while DBG() macro itself does this anyway;
most of these were added by commit f11d893d
(usb: musb: support ISO high bandwidth for gadget mode). Remove the duplicated
printing, somewhat clarifying the messages at the same time...

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>