md: fix return value of mddev_trylock

md: fix return value of mddev_trylock

A return value of 0 is treaded as successful lock acquisition. In fact, a
return value of 1 means getting the lock successfully.

Link: https://lore.kernel.org/linux-raid/20260127073951.17248-1-xni@redhat.com
Fixes: 9e59d609763f ("md: call del_gendisk in control path")
Reported-by: Bart Van Assche <bvanassche@acm.org>
Closes: https://lore.kernel.org/linux-raid/20250611073108.25463-1-xni@redhat.com/T/#mfa369ef5faa4aa58e13e6d9fdb88aecd862b8f2f
Signed-off-by: Xiao Ni <xni@redhat.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by:  Li Nan <linan122@huawei.com>
Signed-off-by: Yu Kuai <yukuai@fnnas.com>