umc-bus.c: fix usage of device_trylock

Fix usage of device_trylock. It has the same semantics of mutex_trylock, so it
returns 1 if the lock has been acquired successfully.

Signed-off-by: Claudio Scordino <claudio@evidence.eu.com>
Signed-off-by: Bruno Morelli <bruno@evidence.eu.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>