mips: bcm63xx: add support for clk_set_parent()

The MIPS BMC63XX subarch does not provide/support clk_set_parent().
This causes build errors in a few drivers, so add a simple implementation
of that function 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: e7300d04 ("MIPS: BCM63xx: Add support for the Broadcom BCM63xx family of SOCs." )
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>