libs/utils/energy: Fix error reporting for missing hwmon channel
libs/utils/energy: Fix error reporting for missing hwmon channel

For some platforms (e.g., JunoR2) channel labels in the energy report
might differ from channel names, and this raises a runtime error (even
if energy is correctly reported).

Fix it by always use channel labels.

Fixes: a41a48dfabb7 ('libs/utils/energy: Slightly improve error for missing hwmon channel')
Signed-off-by: Juri Lelli <bdc6bcd4e8b34b4b92413d758024aeca6da0e459@arm.com>

mdigiorgio/lisa,credp/lisa,bjackman/lisa,mdigiorgio/lisa,credp/lisa,credp/lisa,arnoldlu/lisa,ARM-software/lisa,credp/lisa,bjackman/lisa,ARM-software/lisa,ARM-software/lisa,arnoldlu/lisa,ARM-software/lisa