USB: dummy-hcd: increase max number of devices to 32

USB: dummy-hcd: increase max number of devices to 32

When fuzzing the USB subsystem with syzkaller, we currently use 8 testing
processes within one VM. To isolate testing processes from one another it
is desirable to assign a dedicated USB bus to each of those, which means
we need at least 8 Dummy UDC/HCD devices.

This patch increases the maximum number of Dummy UDC/HCD devices to 32
(more than 8 in case we need more of them in the future).

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Link: https://lore.kernel.org/r/665578f904484069bb6100fb20283b22a046ad9b.1571667489.git.andreyknvl@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>