New review comment by sgn on void-packages repository

https://github.com/void-linux/void-packages/pull/40128#discussion_r1007879223

Comment:
>        -E, -r, --regexp-extended
>
>              use extended regular expressions in the script (for portability
>              use POSIX -E).

But the whole line can be rewrite to a single awk
```sh
awk '$1 ~ /^UUID=/ && $2 == "/" { sub(/^UUID=/, "", $1); print $1 }' /etc/fstab
# or
awk '$1 ~ /^UUID=/ && $2 == "/" { $1=substr($1, 6); print $1 }' /etc/fstab
```