vhost: fix guest/host physical address conversion

vhost: fix guest/host physical address conversion

gpa_to_hpa() function almost always fails due to the wrong setup of
the binary tree search key. Since there has already been a similar
function gpa_to_first_hpa() available in the vhost, instead of fixing
the issue in its original logic, gpa_to_hpa() function is rewritten to
be a wrapper of the gpa_to_first_hpa() to avoid code redundancy.

Fixes: e246896178e6 ("vhost: get guest/host physical address mappings")
Fixes: faa9867c4da2 ("vhost: use binary search in address conversion")
Cc: stable@dpdk.org
Signed-off-by: Patrick Fu <patrick.fu@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>