lib/cmdline: Update documentation to reflect behaviour

get_options() API has some tricks to optimize that may be not so obvious
to the caller. Update documentation to reflect current behaviour.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>

lib/cmdline.c

@@ -83,7 +83,7 @@ EXPORT_SYMBOL(get_option);
  *	get_options - Parse a string into a list of integers
  *	@str: String to be parsed
  *	@nints: size of integer array
- *	@ints: integer array
+ *	@ints: integer array (must have room for at least one element)
  *
  *	This function parses a string containing a comma-separated
  *	list of integers, a hyphen-separated range of _positive_ integers,
@@ -91,6 +91,11 @@ EXPORT_SYMBOL(get_option);
  *	full, or when no more numbers can be retrieved from the
  *	string.
  *
+ *	Returns:
+ *
+ *	The first element is filled by the number of collected integers
+ *	in the range. The rest is what was parsed from the @str.
+ *
  *	Return value is the character in the string which caused
  *	the parse to end (typically a null terminator, if @str is
  *	completely parseable).