Staging: rt2860: Makefile: cleaned up Makefile cflag lines

Changed to use the proper ccflags-y option

Signed-off-by: Tracey Dent <tdent48227@gmail.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>