block: fix get_max_segment_size() warning

Correct the parameter name in the comment of get_max_segment_size()
to fix following warning:-

block/blk-merge.c:220: warning: Function parameter or struct member 'len' not described in 'get_max_segment_size'
block/blk-merge.c:220: warning: Excess function parameter 'max_len' description in 'get_max_segment_size'
Signed-off-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20240709045432.8688-1-kch@nvidia.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-merge.c

@@ -210,7 +210,7 @@ static inline unsigned get_max_io_size(struct bio *bio,
  * get_max_segment_size() - maximum number of bytes to add as a single segment
  * @lim: Request queue limits.
  * @paddr: address of the range to add
- * @max_len: maximum length available to add at @paddr
+ * @len: maximum length available to add at @paddr
  *
  * Returns the maximum number of bytes of the range starting at @paddr that can
  * be added to a single segment.