block: use the %pg format specifier in show_partition

Simplify printing the partition name by using the %pg format specifier
that is equivalent to a bdevname call.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20210727062518.122108-4-hch@lst.de


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