mount.2: minor fix: write "file system" as two words (not "filesystem")

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/mount.2

@@ -287,7 +287,7 @@ is set appropriately.
 .SH ERRORS
 The error values given below result from filesystem type independent
 errors.
-Each filesystem type may have its own special errors and its
+Each file-system type may have its own special errors and its
 own special behavior.
 See the kernel source code for details.
 .TP
@@ -295,12 +295,12 @@ See the kernel source code for details.
 A component of a path was not searchable.
 (See also
 .BR path_resolution (7).)
-Or, mounting a read-only filesystem was attempted without giving the
+Or, mounting a read-only file system was attempted without giving the
 .B MS_RDONLY
 flag.
 Or, the block device
 .I source
-is located on a filesystem mounted with the
+is located on a file system mounted with the
 .B MS_NODEV
 option.
 .\" mtk: Probably: write permission is required for MS_BIND, with
@@ -403,7 +403,7 @@ when a different
 was added to \fI<mman.h>\fP.
 .LP
 Before Linux 2.4 an attempt to execute a set-user-ID or set-group-ID program
-on a filesystem mounted with
+on a file system mounted with
 .B MS_NOSUID
 would fail with
 .BR EPERM .