block: pre-initialize struct block_device in bdev_alloc_inode

block: pre-initialize struct block_device in bdev_alloc_inode

bdev_evict_inode and bdev_free_inode are also called for the root inode
of bdevfs, for which bdev_alloc is never called.  Move the zeroing o
f struct block_device and the initialization of the bd_bdi field into
bdev_alloc_inode to make sure they are initialized for the root inode
as well.

Fixes: e6cb53827ed6 ("block: initialize struct block_device in bdev_alloc")
Reported-by: Alexey Kardashevskiy <[email protected]>
Tested-by: Alexey Kardashevskiy <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>