usb: musb: dsps: make it depend on OF_IRQ

musb_dsps.c utilizes a symbol which is only
available when CONFIG_OF_IRQ is set, so make
it depend on that.
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/musb/Kconfig

@@ -84,6 +84,7 @@ config USB_MUSB_AM35X
 config USB_MUSB_DSPS
 	tristate "TI DSPS platforms"
 	select USB_MUSB_AM335X_CHILD
+	depends on OF_IRQ
 
 config USB_MUSB_BLACKFIN
 	tristate "Blackfin"