thermal: cpu_cooling: fix stub function

The function stub for cpufreq_cooling_get_level introduced
in 57df8106 "Thermal: exynos: fix cooling state translation"
is not syntactically correct C and needs to be fixed to avoid
this error:

In file included from drivers/thermal/db8500_thermal.c:20:0:
 include/linux/cpu_cooling.h: In function 'cpufreq_cooling_get_level':
include/linux/cpu_cooling.h:57:1:
 error: parameter name omitted  unsigned long cpufreq_cooling_get_level(unsigned int, unsigned int)  ^
 include/linux/cpu_cooling.h:57:1: error: parameter name omitted

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Eduardo Valentin <eduardo.valentin@ti.com>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Amit Daniel kachhap <amit.daniel@samsung.com>
Cc: stable@vger.kernel.org
Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>