tests/avocado/hotplug_blk: Fix addr in device_add command

tests/avocado/hotplug_blk: Fix addr in device_add command

pci_devfn properties accept both integer and string values, but
integer 1 and string '1' have different meanings: The integer value
means device 0, function 1 whereas the string value '1' is short for
'1.0' and means device 1, function 0.

This test wants the string version so that the device actually becomes
visible for the guest. device_add hides the problem because it goes
through QemuOpts, which turns all properties into strings - this is a
QEMU bug that we want to fix, but that cancelled out the bug in this
test.

Fix the test first so that device_add can be fixed afterwards.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20241122224042.149258-1-kwolf@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>