lib/bitmap: Fix bitmap_scatter() and bitmap_gather() kernel doc

lib/bitmap: Fix bitmap_scatter() and bitmap_gather() kernel doc

The make htmldoc command failed with the following error
  ... include/linux/bitmap.h:524: ERROR: Unexpected indentation.
  ... include/linux/bitmap.h:524: CRITICAL: Unexpected section title or transition.

Move the visual representation to a literal block.

Fixes: de5f84338970 ("lib/bitmap: Introduce bitmap_scatter() and bitmap_gather() helpers")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Closes: https://lore.kernel.org/linux-kernel/20240312153059.3ffde1b7@canb.auug.org.au/
Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Acked-by: Yury Norov <yury.norov@gmail.com>
Link: https://lore.kernel.org/r/20240314120006.458580-1-herve.codina@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>