I'm not sure I understand your problem. Is it that the camera app won't start? That happened to me once after I colored black the little white stripe on the inside of the back cover of the phone. A piece of white tape fixed the problem.
That interface is read only, by reading it you are calling rx51_show_shutter() which reads the gpio. Look at the file arch/arm/mach-omap2/rx51_camera_btn.c You'll need to modify rx51_show_shutter() and if you want a writable interface you need to add a function to write it.