db: split function call returns if we can

db: split function call returns if we can

Say you have code like:

int my_frob(int whatevever)
{
	return frob(whatever);
}

We probably try to break frob()'s returns up into separate strees.  But
then the my_frob() function just merges them all together.

With this patch we preserve the strees and keep them separated.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>