mips: lantiq: add support for clk_set_parent()

mips: lantiq: add support for clk_set_parent()

Provide a simple implementation of clk_set_parent() in the lantiq
subarch so that callers of it will build without errors.

Fixes these build errors:

ERROR: modpost: "clk_set_parent" [sound/soc/jz4740/snd-soc-jz4740-i2s.ko] undefined!
ERROR: modpost: "clk_set_parent" [sound/soc/atmel/snd-soc-atmel-i2s.ko] undefined!

Fixes: 171bb2f19ed6 ("MIPS: Lantiq: Add initial support for Lantiq SoCs")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <lkp@intel.com>
--to=linux-mips@vger.kernel.org --cc="John Crispin <john@phrozen.org>" --cc="Jonathan Cameron <jic23@kernel.org>" --cc="Russell King <linux@armlinux.org.uk>" --cc="Andy Shevchenko <andy.shevchenko@gmail.com>" --cc=alsa-devel@alsa-project.org --to="Thomas Bogendoerfer <tsbogend@alpha.franken.de>"
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>