ACPICA: getopt: Comment update, no functional change

ACPICA commit 0d784a90bc3aac75227c4459c3553de18b9ebe7a

Document one of the option string operators.

Link: https://github.com/acpica/acpica/commit/0d784a90
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

tools/power/acpi/common/getopt.c

@@ -47,6 +47,7 @@
  * Option strings:
  *    "f"       - Option has no arguments
  *    "f:"      - Option requires an argument
+ *    "f+"      - Option has an optional argument
  *    "f^"      - Option has optional single-char sub-options
  *    "f|"      - Option has required single-char sub-options
  */