sysctl(2) man page typo correction

[Piotr Durlej]

--- lib/libc/sys/sysctl.2.old   Tue Nov  6 10:08:56 2018
+++ lib/libc/sys/sysctl.2       Tue Nov  6 10:09:03 2018
@@ -256,7 +256,7 @@
 .It Dv FS_POSIX_SETUID Ta "integer" Ta "yes"
 .El
 .Bl -tag -width "123456"
-.It Dv FS_POSIX_SETUID Pq Va fx.posix.setuid
+.It Dv FS_POSIX_SETUID Pq Va fs.posix.setuid
 When this variable is set, ownership changes on a file will cause
 the
 .Va S_ISUID