[6.9.2] Fix for Unassigned Devices temperature notifications

tl;dr: It appears to me that Unraid 6.9.2 doesn't honor device-specific temperature notification settings for Unassigned Devices for a straightforward reason that is easily fixed.

Now that I have two unassigned NVME drives in my Unraid server, the annoyance of over-temp notifications that ignore the per-device settings has doubled, so I've come up with what is hopefully a true fix, rather than a workaround, in the form of a small change to the check_temp function in /usr/local/emhttp/plugins/dynamix/scripts/monitor.

Here's the diff for /usr/local/emhttp/plugins/dynamix/scripts/monitor in Unraid 6.9.2:

61,62c61,66
<   global $notify,$disks,$saved,$display,$server,$top;
<   $disk = &$disks[$name];
---
>   global $notify,$disks,$devs,$saved,$display,$server,$top;
>   if (isset($disks[$name])) {
>     $disk = &$disks[$name];
>   } else {
>     $disk = &$devs[$name];
>   }

The logic behind the change is that it appears to me that while the $devs array does properly include the hotTemp ("Warning disk temperature threshold") and maxTemp ("Critical disk temperature threshold") values as a result of CustomMerge.php merging them from the /boot/config/smart-one.cfg file, the check_temp function in 6.9.2 fails to consider the $devs array at all.

This patch changes check_temp so that $devs is included as a global, so that if the passed $name can't be found in the $disks array, a lookup in $devs can be attempted, instead.

I suspect there's a more elegant way to implement the fallback from $disks to $devs, but I'll leave that as an exercise for people who know PHP well 

I don't claim this to be well-researched or production-quality code, but it does fundamentally make sense, and It Works On My System™, so I hope this is helpful.