clockevents: Fix syntax error in clkevt-of macro

The patch fix syntax errors introduced by commit 0c8893c9095d
("clockevents: Add a clkevt-of mechanism like clksrc-of").

Fixes: 0c8893c9095d ("clockevents: Add a clkevt-of mechanism like clksrc-of")
Signed-off-by: Alexander Kochetkov <al.kochet@gmail.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>