usb: hub: Fix flushing of delayed work used for post resume purposes

usb: hub: Fix flushing of delayed work used for post resume purposes

Delayed work that prevents USB3 hubs from runtime-suspending too early
needed to be flushed in hub_quiesce() to resolve issues detected on
QC SC8280XP CRD board during suspend resume testing.

This flushing did however trigger new issues on Raspberry Pi 3B+, which
doesn't have USB3 ports, and doesn't queue any post resume delayed work.

The flushed 'hub->init_work' item is used for several purposes, and
is originally initialized with a 'NULL' work function. The work function
is also changed on the fly, which may contribute to the issue.

Solve this by creating a dedicated delayed work item for post resume work,
and flush that delayed work in hub_quiesce()

Cc: stable <stable@kernel.org>
Fixes: a49e1e2e785f ("usb: hub: Fix flushing and scheduling of delayed work that tunes runtime pm")
Reported-by: Mark Brown <broonie@kernel.org>
Closes: https://lore.kernel.org/linux-usb/aF5rNp1l0LWITnEB@finisterre.sirena.org.uk
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Tested-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com> # SC8280XP CRD
Tested-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20250627164348.3982628-2-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>