ARM: SAMSUNG: Add check to ensure that clksrc_clk does have multiple clock sources

Adds a additional check in s3c_set_clksrc function to ensure that the clksrc_clk
does have a choice of multiple clock sources. In addition to this, a check is
added to ensure that a parent is assigned to the clksrc_clk in case it does not
have a choice of parent clocks.

Signed-off-by: Thomas Abraham <thomas.ab@samsung.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>