clocksource/drivers/lpc32: Correct pr_err() output format

If by some reason timerclk is not available, both clockevent and
clocksource initializations correctly exit, but output of errno to
kernel log buffer may be confusing:

  lpc32xx_clk_init: failed to map system control block registers
  lpc32xx_clocksource_init: clock get failed (4294966779)
  lpc32xx_clockevent_init: clock get failed (4294966779)

Use signed integer output in the correspondent pr_err() string formats:

  lpc32xx_clocksource_init: clock get failed (-517)
  lpc32xx_clockevent_init: clock get failed (-517)

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>