clk: Return void from debug_init op

We only have two users of the debug_init hook, and we recently stopped
caring about the return value from that op. Finish that off by changing
the clk_op to return void instead of int because it doesn't matter if
debugfs fails or not.

Cc: Eric Anholt <eric@anholt.net>
Cc: David Lechner <david@lechnology.com>
Cc: Sekhar Nori <nsekhar@ti.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>