nvme: explicitly update mpath disk capacity on revalidation

Commit 3b4b1972 ("nvme: fix possible deadlock when I/O is
blocked") reverted multipath head disk revalidation due to deadlocks
caused by holding the bd_mutex during revalidate.

Updating the multipath disk blockdev size is still required though for
userspace to be able to observe any resizing while the device is
mounted. Directly update the bdev inode size to avoid unnecessarily
holding the bdev->bd_mutex.

Fixes: 3b4b1972 ("nvme: fix possible deadlock when I/O is
blocked")

Signed-off-by: Anthony Iliopoulos <ailiop@suse.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>