USB: musb: minor locking fix

Minor locking fix for musb_hdrc on OMAP3 and OMAP2430:
don't read DEVCTL without holding the spinlock, since
an IRQ could come in and corrupt things.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>