[RFC] nvme: set block size during namespace validation

[Christoph Hellwig]

set_blocksize just sets the block sise used for buffer heads and should
not be called by the driver.  blkdev_get updates the block size, so
you must already have the fd re-reading the partition table open?
I'm not entirely sure how we can work around this except by avoiding
buffer head I/O in the partition reread code.  Note that this affects
all block drivers where the block size could change at runtime.