diff: fix incorrectly displaying files as duplicates

When diff hits certain access errors, function diffreg() shows the error
message, and then returns to the calling function, which calls
print_status() with the return value.

However, in these cases, the return value isn't changed from the initial
default value of D_SAME.

Normally, print_status() with a value of D_SAME does nothing, so this
works out ok, however, if the "-s" flag is set, a message is displayed
showing identicality:

case D_SAME:
                if (sflag)
                        printf("Files %s%s and %s%s are identical\n",                                                                                                       path1, entry, path2, entry);
                break;

This then produces such results as:

% diff  -s /COPYRIGHT /var/run/rpcbind.sock
diff: /var/run/rpcbind.sock: Operation not supported
Files /COPYRIGHT and /var/run/rpcbind.sock are identical

% diff  -s /COPYRIGHT /etc/master.passwd
diff: /etc/master.passwd: Permission denied
Files /COPYRIGHT and /etc/master.passwd are identical

Create a D_ERROR status which is returned in such cases, and
print_status() then deals with that status seperately from D_SAME

PR:		252614
MFC after:	1 week

1 files changed, 2 insertions, 0 deletions

diff --git a/usr.bin/diff/diff.c b/usr.bin/diff/diff.c
index 0e46b96f9667..1bad6226f49d 100644
--- a/usr.bin/diff/diff.c
+++ b/usr.bin/diff/diff.c
@@ -511,6 +511,8 @@ print_status(int val, char *path1, char *path2, const char *entry)
 		printf("File %s%s is not a regular file or directory and was skipped\n",
 		    path2, entry);
 		break;
+	case D_ERROR:
+		break;
 	}
 }