null_blk: don't initialize static 'g_virt_boundary' to false

No functional changes intended.

Signed-off-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Link: https://lore.kernel.org/r/20240704010638.324349-1-yanjun.zhu@linux.dev


Signed-off-by: Jens Axboe <axboe@kernel.dk>