vfs: Update fs.h to use inline functions when no file locking set

This avoids various issues which might give rise to compiler warnings
about missing functions and/or unused variable with the previous
macros. This also fixes a bug where one of the macros was returning
0, but it should have been void.

Reported-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Tested-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>