P2PS: Fix attribute addition in p2p_buf_add_service_instance()

P2PS: Fix attribute addition in p2p_buf_add_service_instance()

Fix a condition when Advertised Service Info Attribute is added to
a probe response in p2p_buf_add_service_instance(). The issue is
that a 'found' value is increased even if 'test' and 'adv->hash' hashes
are different. As result 'found' may have a non-zero value when an
attribute data length is 0. In this cause an empty attribute is about to
be added. Fixing it by eliminating 'found' and checking 'total_len'
containing a real number of bytes added to Advertised Service Info
Attribute.

This fixes an issue from commit 50a9efe713df135e98f2229f67faa1a3d7243693
('P2PS: Fix Probe Response frame building in error cases').

Signed-off-by: Max Stepanov <Max.Stepanov@intel.com>