deflate_mutex protects the globals lzo_mem and lzo_compress_buf.  However,
jffs2_lzo_compress() unlocks deflate_mutex _before_ it has copied out the
compressed data from lzo_compress_buf.  Correct this by moving the mutex
unlock after the copy.

In addition, document what deflate_mutex actually protects.

Cc: stable@kernel.org
Signed-off-by: NGeert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Acked-by: NRichard Purdie <rpurdie@openedhand.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NDavid Woodhouse <David.Woodhouse@intel.com>