USB: musb: fix session-bit runtime-PM quirk

USB: musb: fix session-bit runtime-PM quirk

BugLink: http://bugs.launchpad.net/bugs/1731951
commit 4f190e0b9de89c4c917c3ffb3799e9d00fc534ac upstream.

The current session-bit quirk implementation does not prevent the retry
counter from underflowing, something which could break runtime PM and
keep the device active for a very long time (about 2^32 seconds) after a
disconnect.

This notably breaks the B-device timeout case, but could potentially
cause problems also when the controller is operating as an A-device.

Fixes: 2bff3916fda9 ("usb: musb: Fix PM for hub disconnect")
Cc: Tony Lindgren <tony@atomide.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Tested-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>