thermal: cpu_cooling: fix 'descend' check in get_property()

The variable 'descend' is initialized as -1 in function get_property(),
and will never get any chance to be updated by the following code.

	if (freq != CPUFREQ_ENTRY_INVALID && descend != -1)
		descend = !!(freq > table[i].frequency);

This makes function get_property() return the wrong frequency for given
cooling level if the frequency table is sorted in ascending.  Fix it
by correcting the 'descend' check in if-condition to 'descend == -1'.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>