i2c: pnx: Disable clk in suspend

In the driver's suspend function, clk_enable() was used instead of
clk_disable(). This is corrected with this patch.

Signed-off-by: Roland Stigge <stigge@antcom.de>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
CC: stable@vger.kernel.org