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>
diff --git a/drivers/usb/musb/Kconfig b/drivers/usb/musb/Kconfig
index 04658d7..c64ee09a7 100644
--- a/drivers/usb/musb/Kconfig
+++ b/drivers/usb/musb/Kconfig
@@ -84,6 +84,7 @@
 config USB_MUSB_DSPS
 	tristate "TI DSPS platforms"
 	select USB_MUSB_AM335X_CHILD
+	depends on OF_IRQ
 
 config USB_MUSB_BLACKFIN
 	tristate "Blackfin"