clk: test: Fix type sign of rounded rate variables

clk_round_rate() may return a negative error code, but most of the
variables we defined to store its returned value are unsigned.

This obviously leads to issues on error.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20221018-clk-range-checks-fixes-v4-2-971d5077e7d2@cerno.tech


Signed-off-by: Stephen Boyd <sboyd@kernel.org>