clk: Propagate any error return from debug_init()

If the .debug_init op is provided, it will be called by
clk_debug_create_one(). If debug_init() returns an error code,
clk_debug_create_one() will return -ENOMEM, regardless of the
value returned from debug_init(). Tweak the code to return
the actual value returned by debug_init() instead.

Signed-off-by: Chris Brand <chris.brand@linaro.org>
Reviewed-by: Matt Porter <mporter@linaro.org>
Reviewed-by: Alex Elder <elder@linaro.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>