thermal: devfreq_cooling: Fix kernel-doc

Fix function name in devfreq_cooling.c comment to remove a
warning found by kernel-doc.

drivers/thermal/devfreq_cooling.c:479: warning: expecting prototype for
devfreq_cooling_em_register_power(). Prototype was for
devfreq_cooling_em_register() instead.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/1623223350-128104-1-git-send-email-yang.lee@linux.alibaba.com