db: fix ignoring wrong callers

db: fix ignoring wrong callers

We ignore callers if the prototypes don't match.  This normally happens
with function pointers because there can be two (struct struct_name)->frob
pointers, but the parameters are different.

It should be ignoring after func_id != data->prev_func_id otherwise it's
looking at the wrong caller.

Then after handling the direct_callers we should to a merge of that tree.
Probably there aren't that many functions that have both direct and function
pointer callers so that's why I didn't notice this before.

Also there was a one merge where we should have been checking ignore before
doing the merge.

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