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: de5f8433 ("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.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/bitmap.h

@@ -522,7 +522,8 @@ static inline void bitmap_replace(unsigned long *dst,
  *
  * (Bits 0, 1, 2, 3, 4, 5 are copied to the bits 0, 1, 4, 8, 9, 12)
  *
- * A more 'visual' description of the operation:
+ * A more 'visual' description of the operation::
+ *
  *	src:  0000000001011010
  *	                ||||||
  *	         +------+|||||
@@ -568,7 +569,8 @@ static inline void bitmap_scatter(unsigned long *dst, const unsigned long *src,
  *
  * (Bits 0, 1, 4, 8, 9, 12 are copied to the bits 0, 1, 2, 3, 4, 5)
  *
- * A more 'visual' description of the operation:
+ * A more 'visual' description of the operation::
+ *
  *	mask: ...v..vv...v..vv
  *	src:  0000001100000010
  *	         ^  ^^   ^   0