The omap musb front-end calls into the phy driver directly
instead of using a generic phy interface, which causes a link
error when the specific driver is not built-in:

drivers/built-in.o: In function `omap2430_musb_disable':
usb/musb/omap2430.c:480: undefined reference to `omap_control_usb_set_mode'
drivers/built-in.o: In function `omap2430_musb_enable':
usb/musb/omap2430.c:466: undefined reference to `omap_control_usb_set_mode'
usb/musb/omap2430.c:447: undefined reference to `omap_control_usb_set_mode'
drivers/built-in.o: In function `omap_musb_set_mailbox':
usb/musb/omap2430.c:273: undefined reference to `omap_control_usb_set_mode'
usb/musb/omap2430.c:304: undefined reference to `omap_control_usb_set_mode'
drivers/built-in.o:(.debug_addr+0xbd9e0): more undefined references to `omap_control_usb_set_mode' follow

This adds an explicit dependency.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: ca784be3 ("usb: start using the control module driver")
Cc: <stable@vger.kernel.org> # v3.9+
Signed-off-by: Felipe Balbi <balbi@ti.com>