USB Gadget: Verify VBUS current before setting the device self-powered bit

Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Praveena Nadahally <praveen.nadahally@stericsson.com>
Signed-off-by: Parirajan Muthalagu <parirajan.muthalagu@stericsson.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>