USB: musb: fix Blackfin ulpi stubs

The new ulpi code defines fallback stubs for the Blackfin arch, but does
so incorrectly leading to a build failure:
drivers/usb/musb/musb_core.c:227: error: 'musb_ulpi_read' undeclared here (not in a function)
drivers/usb/musb/musb_core.c:228: error: 'musb_ulpi_write' undeclared here (not in a function)

Tweak the fallback stubs so that they do work as intended.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Ajay Kumar Gupta <ajay.gupta@ti.com>
Acked-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>