armv7: fix syscall to get the ticks per ms.
armv7: fix syscall to get the ticks per ms.

fixes commit 4787e75a4f4d

sys_debug_get_tsc_per_ms() is used throughout the entire
Barrelfish source tree.

Signed-off-by: Reto Achermann <66f6ea3e040423755b3cf26edfe6c7fb1f9adc27@inf.ethz.ch>

kishoredbn/barrelfish,kishoredbn/barrelfish,kishoredbn/barrelfish,BarrelfishOS/barrelfish,BarrelfishOS/barrelfish,BarrelfishOS/barrelfish,BarrelfishOS/barrelfish,BarrelfishOS/barrelfish,BarrelfishOS/barrelfish,kishoredbn/barrelfish,kishoredbn/barrelfish,BarrelfishOS/barrelfish,BarrelfishOS/barrelfish,kishoredbn/barrelfish,BarrelfishOS/barrelfish