fs/efs: return f_fsid for statfs(2)

Make efs return f_fsid info for statfs(2), and do a little variable
renaming in efs_statfs().

Signed-off-by: Coly Li <coly.li@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>