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>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>