docs: fix double parens in internal link

Signed-off-by: David Karlsson <[email protected]>

Author: dvdksn

frontend/dockerfile/docs/reference.md

@@ -347,7 +347,7 @@ despite warnings. To make the build fail on warnings, set `#check=error=true`.
 
 > [!NOTE]
 > When using the `check` directive, with `error=true` option, it is recommended
-> to pin the [Dockerfile syntax]((#syntax)) to a specific version. Otherwise, your build may
+> to pin the [Dockerfile syntax](#syntax) to a specific version. Otherwise, your build may
 > start to fail when new checks are added in the future versions.
 
 To combine both the `skip` and `error` options, use a semi-colon to separate