global_data: Fix comment for dm_driver_rt

This comment is in the wrong format, so reports an error with
'make htmldocs'. Fix it.

Fixes: a294ead8 ("dm: Use an allocated array for run-time device info")
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>