USB: musb: Kconfig fix

The Blackfin MUSB Kconfig text didn't properly parenthesise its
dependencies.  This was visible in non-Blackfin configs by the
way the user interfaces lost track of dependencies, when doing
a bunch of test builds.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>