GP Timers used as clockevent/source are not available for ti-sysc bus and
handled by Kernel timekeeping core. Now ti-sysc produces error message
every time such timer is detected:

 "ti-sysc: probe of 48040000.target-module failed with error -16"

Such messages are not necessary, so suppress them by returning -ENXIO
instead of -EBUSY.

Fixes: 6cfcd556 ("clocksource/drivers/timer-ti-dm: Fix suspend and resume for am3 and am4")
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>