clocksource/drivers/atmel-pit: Fix compilation error

clocksource/drivers/atmel-pit: Fix compilation error

The previous fix introduced a check against the ret variable which
is not defined, hence producing a compilation error:

linux/drivers/clocksource/timer-atmel-pit.c: In function ‘at91sam926x_pit_dt_init’:
linux/drivers/clocksource/timer-atmel-pit.c:264:2: error: ‘ret’ undeclared (first use in this function)
  ret = clk_prepare_enable(data->mck);
  ^
linux/drivers/clocksource/timer-atmel-pit.c:264:2: note: each undeclared identifier is reported only once for each function it appears in

Add the missing the variable 'ret'.

Fixes: 504f34c9e45c "clocksource/drivers/atmel-pit: Convert init function to return error"
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: alexandre.belloni@free-electrons.com
Cc: motobud@gmail.com
Cc: realbright@lgcns.com
Link: http://lkml.kernel.org/r/1472453043-24287-1-git-send-email-daniel.lezcano@linaro.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>