docs: block: fix discard_max_bytes references

When discard_max_hw_bytes was introduced, in commit 0034af03
("block: make /sys/block/<dev>/queue/discard_max_bytes writeable"),
the discard_max_bytes documentation section was renamed to
discard_max_hw_bytes, but the references it contains to
discard_max_bytes weren't updated.

This patch refers to discard_max_hw_bytes instead. It also reflows the
paragraph so that sentences end lines.
Signed-off-by: Stephen Kitt <steve@sk2.org>
Link: https://lore.kernel.org/r/20210910105142.2116749-1-steve@sk2.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/block/queue-sysfs.rst

@@ -40,10 +40,11 @@ discard_max_hw_bytes (RO)
 -------------------------
 Devices that support discard functionality may have internal limits on
 the number of bytes that can be trimmed or unmapped in a single operation.
-The discard_max_bytes parameter is set by the device driver to the maximum
-number of bytes that can be discarded in a single operation. Discard
-requests issued to the device must not exceed this limit. A discard_max_bytes
-value of 0 means that the device does not support discard functionality.
+The `discard_max_hw_bytes` parameter is set by the device driver to the
+maximum number of bytes that can be discarded in a single operation.
+Discard requests issued to the device must not exceed this limit.
+A `discard_max_hw_bytes` value of 0 means that the device does not support
+discard functionality.
 
 discard_max_bytes (RW)
 ----------------------