Documentation: admin-guide: blockdev: replace zone_capacity with zone_capacity_mb when creating devices

The "zone_capacity=%umb" option is no longer used. The effective option
is now "zone_capacity_mb=%u", so update the documentation accordingly.

Signed-off-by: Yongpeng Yang <yangyongpeng@xiaomi.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Yongpeng Yang

Documentation/admin-guide/blockdev/zoned_loop.rst

@@ -134,7 +134,7 @@ MB and a zone capacity of 63 MB::
 
         $ modprobe zloop
         $ mkdir -p /var/local/zloop/0
-        $ echo "add capacity_mb=2048,zone_size_mb=64,zone_capacity=63MB" > /dev/zloop-control
+        $ echo "add capacity_mb=2048,zone_size_mb=64,zone_capacity_mb=63" > /dev/zloop-control
 
 For the device created (/dev/zloop0), the zone backing files are all created
 under the default base directory (/var/local/zloop)::