util: add missing DRI_CONF_OPT_END

When DRI_CONF_GLES_EMULATE_BGRA was added for the virgl driver, it
missed a DRI_CONF_OPT_END.

This make some drivers, like v4c/v3d to crash with the following
error:
Fatal error in __driConfigOptions line 99, column 2: mismatched tag.

Not sure why it doesn't fail with virgl.

Fixes: b793663449
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>

src/util/xmlpool/t_options.h

@@ -361,6 +361,7 @@ DRI_CONF_OPT_END
 #define DRI_CONF_V3D_NONMSAA_TEXTURE_SIZE_LIMIT(def) \
 DRI_CONF_OPT_BEGIN_B(v3d_nonmsaa_texture_size_limit, def) \
         DRI_CONF_DESC(en,"Report the non-MSAA-only texture size limit") \
+DRI_CONF_OPT_END
 /**
  * \brief virgl specific configuration options
  */