clk: Simplify clk_core_can_round()

A boolean expression already evaluates to true or false, so there is no
need to check the result and return true or false explicitly.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>