clocksource/drivers/time-armada-370-xp: Fix return value check

clocksource/drivers/time-armada-370-xp: Fix return value check

The failure check of armada_370_xp_timer_setup() in
armada_370_xp_timer_common_init() is negated. This leads to an error message
and exit in case of a successful initialization.  Remove the stray '!'.

Fixes: d01d8d1b823c ("clocksource/drivers/time-armada-370-xp: Convert init function to return error")
Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1607121731020.1344@hypnos.tec.linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>