fsi: Improve master indexing

Master indexing is problematic if a hub is rescanned while the
root master is being rescanned. Always allocate an index for the
FSI master, and set the device name if it hasn't already been set.
Move the call to ida_free to the bottom of master unregistration
and set the number of links to 0 in case another call to scan
comes in before the device is removed.

Signed-off-by: Eddie James <eajames@linux.ibm.com>
Link: https://lore.kernel.org/r/20230809180814.151984-2-eajames@linux.ibm.com


Signed-off-by: Joel Stanley <joel@jms.id.au>