clk: Ignore disabled DT clock providers

of_clk_init() uses for_each_matching_node_and_match() to find clock
providers, which returns all matching device nodes, whether they are
enabled or not. Hence clock providers that are disabled explicitly in DT
using e.g.

	"status = "disabled";

are still activated.

Add a check to ignore device nodes that are not enabled, like
of_irq_init() does.

Reported-by: Ramesh Shanmugasundaram <ramesh.shanmugasundaram@bp.renesas.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>