The 'osc' clock is already initialized by the fixed clock defined in
imx25.dtsi. The imx25 clock driver tries to add this clock for a second
time and fails with -EEXIST:
	i.MX clk 1: register failed with -17

As the clock is already properly setup in DT with a different driver, we
can completely remove the handling in the imx25 clock driver.
Signed-off-by: NMarkus Pargmann <mpa@pengutronix.de>
Reviewed-by: NLucas Stach <l.stach@pengutronix.de>
Signed-off-by: NShawn Guo <shawnguo@kernel.org>