clk: bcm-2835: Pick the closest clock rate

The driver currently tries to pick the closest rate that is lower than
the rate being requested.

This causes an issue with clk_set_min_rate() since it actively checks
for the rounded rate to be above the minimum that was just set.

Let's change the logic a bit to pick the closest rate to the requested
rate, no matter if it's actually higher or lower.

Fixes: 6d18b8ad

 ("clk: bcm2835: Support for clock parent selection")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Reviewed-by: Nicolas Saenz Julienne <nsaenz@kernel.org>
Tested-by: Nicolas Saenz Julienne <nsaenz@kernel.org> # boot and basic functionality
Tested-by: Michael Stapelberg <michael@stapelberg.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210922125419.4125779-2-maxime@cerno.tech