vdpa_sim_blk: remove duplicate include of linux/blkdev.h

In commit 7d189f61 ("vdpa_sim_blk: implement ramdisk behaviour")
linux/blkdev.h was included here causing the duplicate include.
Remove the later duplicate include.

Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Link: https://lore.kernel.org/r/20210510024307.7143-1-wanjiabing@vivo.com


Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>