ci(previews): fix index identifier function

Find operates in breadth-first by default. There can only be one index
per directory. Might as well shorten this find expression to print and
bail out after the first match.

Also resolves the issue where other non-root index files will be picked
as the root index due to sorting precedence.

Signed-off-by: Randolph Sapp <rs@ti.com>

Author: StaticRocket

.github/workflows/deploy.yml

@@ -38,7 +38,7 @@ jobs:
           EOF
 
           for path in build/*/; do
-            root_index=$(find "$path" -name index.html | sort -u | tail -1)
+            root_index=$(find "$path" -name index.html -print -quit)
             if [ -n "$root_index" ]; then
               text=$(basename "$path")
               relative_path=$(realpath "$root_index" --relative-to=build)