usb: musb-new: omap2430: Fix compilation warning with USB_MUSB_GADGET

This commit addresses the following warning, when _NOT_ USB_MUSB_HOST:

[...]
  CC      drivers/usb/gadget/f_mass_storage.o
  CC      drivers/usb/musb-new/omap2430.o
  CC      drivers/usb/gadget/f_fastboot.o
  CC      env/common.o
  CC      env/env.o
/src/etinker/software/u-boot-master/drivers/usb/musb-new/omap2430.c: In function ‘omap2430_musb_probe’:
/src/etinker/software/u-boot-master/drivers/usb/musb-new/omap2430.c:239:6: warning: assignment to ‘int’ from ‘struct musb *’ makes integer from pointer without a cast [-Wint-conversion]
  ret = musb_register(&platdata->plat,
      ^
  LD      drivers/usb/host/built-in.o
  CC      drivers/usb/gadget/f_sdp.o
  CC      fs/ext4/ext4fs.o
[...]

Signed-off-by: Derald D. Woods <woods.technical@gmail.com>