Delete variables 'tree' and 'sb', which are set but never used.

Link: http://lkml.kernel.org/r/1507977146-15875-1-git-send-email-chris.gekas@gmail.comSigned-off-by: Christos Gkekas <chris.gekas@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>