ARM: LPC32XX: Remove broken non-static declaration

This patch fixes a GCC compile error ("static declaration follows non-static
declaration") for LPC32XX's watchdog, removing the extern declaration since
it's not called externally.

Signed-off-by: Roland Stigge <stigge@antcom.de>
Acked-by: Wolfram Sang <w.sang@pengutronix.de>
Acked-by: Kevin Wells <kevin.wells@nxp.com>
Signed-off-by: Olof Johansson <olof@lixom.net>