Until the board specific dts files are updated to have hwmod
flags at the interconnect target module level, we want to keep
things working both for old and new dts files.

So let's also check the first child for hwmod flags. The module
flags are for the whole module, so only the first child should
ever have them.

Cc: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reported-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>