st/mesa: Initialize tgsi_texture_offset Padding field.

Fixes uninitialized scalar variable defect reported by Coverity.

Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: José Fonseca <jfonseca@vmware.com>

src/mesa/state_tracker/st_glsl_to_tgsi.cpp

@@ -4178,6 +4178,7 @@ translate_tex_offset(struct st_translate *t,
    offset.SwizzleX = in_offset->SwizzleX;
    offset.SwizzleY = in_offset->SwizzleY;
    offset.SwizzleZ = in_offset->SwizzleZ;
+   offset.Padding = 0;
 
    return offset;
 }