clk: Simplify debugfs printing and add a newline

The possible parent printing function duplicates a bunch of if
conditions. Pull that into another function so we can print an extra
character at the end, either a space or a newline. This way we can add
the required newline that got lost here and also shorten the code.

Fixes: 2d156b78 ("clk: Fix debugfs clk_possible_parents for clks without parent string names")
Cc: Chen-Yu Tsai <wens@csie.org>
Tested-by: Chen-Yu Tsai <wens@csie.org>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>