tmf: bug 496031 Get the synchronization formula from the original trace

tmf: bug 496031 Get the synchronization formula from the original trace

The synchronize traces handler should get the formula from the original
trace's host ID, not the new one, since the host ID falls back to the trace
name and the new name is different than the original one.

Change-Id: Id4af62b64df4f0b6d042a19e12c04b7e3c060176
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Reviewed-on: https://git.eclipse.org/r/75179
Reviewed-by: Hudson CI
Reviewed-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Tested-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>