isaspec: Remove duplicate return statement.

Fix defect reported by Coverity Scan.

Structurally dead code (UNREACHABLE)
unreachable: This code cannot be reached: return val;.

Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Rob Clark <robclark@freedesktop.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14350>

src/compiler/isaspec/encode.py

@@ -647,7 +647,6 @@ isa = s.isa
       {}  /* in case no unconditional field to close out last '} else' */
     ${case_post(root, case.expr)}
 %endfor
-      return val;
 """
 
 xml = sys.argv[1]