scripts/kernel-doc: restore warning for Excess struct/union

The warning for Excess struct or union member description was
removed when the $nested parameter of check_sections() was removed.
This causes some kernel-doc notation warnings to be missed.

Recently the kernel test robot somehow reported an Excess member. The
code in kernel-doc has not issued that warning since kernel v4.16, so I
don't know how the robot did it. (See the Link for the report.)

  drivers/net/wireless/intel/iwlwifi/fw/dbg.c:86: warning: Excess struct/union/enum/typedef member 'trans_len' description in 'iwl_fw_dump_ptrs'

I patched that warning away even though I could not reproduce the
warning from kernel-doc. The warning should be issued for extraneous
struct member or union member description, so restore it.

Fixes: 1081de2d2f91 ("scripts: kernel-doc: get rid of $nested parameter")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/all/202312060810.QT9zourt-lkp@intel.com/
Cc: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20231214070200.24405-1-rdunlap@infradead.org

scripts/kernel-doc

@@ -1654,6 +1654,13 @@ sub check_sections($$$$$) {
 					"'$sects[$sx]' " .
 					"description in '$decl_name'\n");
 			}
+			elsif (($decl_type eq "struct") or
+		       	       ($decl_type eq "union")) {
+				emit_warning("${file}:$.",
+					"Excess $decl_type member " .
+					"'$sects[$sx]' " .
+					"description in '$decl_name'\n");
+			}
 		}
 	}
 }