checkpatch.pl: Update DT vendor prefix check

In commit 8122de5 ("dt-bindings: Convert vendor prefixes to
json-schema"), vendor-prefixes.txt has been converted to a DT schema.
Update the checkpatch.pl DT check to extract vendor prefixes from the new
vendor-prefixes.yaml file.

Fixes: 8122de5 ("dt-bindings: Convert vendor prefixes to json-schema")
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Rob Herring <robh@kernel.org>

scripts/checkpatch.pl

@@ -3027,7 +3027,7 @@ sub process {
 			my @compats = $rawline =~ /\"([a-zA-Z0-9\-\,\.\+_]+)\"/g;
 
 			my $dt_path = $root . "/Documentation/devicetree/bindings/";
-			my $vp_file = $dt_path . "vendor-prefixes.txt";
+			my $vp_file = $dt_path . "vendor-prefixes.yaml";
 
 			foreach my $compat (@compats) {
 				my $compat2 = $compat;
@@ -3042,7 +3042,7 @@ sub process {
 
 				next if $compat !~ /^([a-zA-Z0-9\-]+)\,/;
 				my $vendor = $1;
-				`grep -Eq "^$vendor\\b" $vp_file`;
+				`grep -Eq "\\"\\^\Q$vendor\E,\\.\\*\\":" $vp_file`;
 				if ( $? >> 8 ) {
 					WARN("UNDOCUMENTED_DT_STRING",
 					     "DT compatible string vendor \"$vendor\" appears un-documented -- check $vp_file\n" . $herecurr);