mm/zsmalloc: add missing annotation for unpin_tag()

mm/zsmalloc: add missing annotation for unpin_tag()

Sparse reports a warning at unpin_tag()()

warning: context imbalance in unpin_tag() - unexpected unlock

The root cause is the missing annotation at unpin_tag()
Add the missing __releases(bitlock) annotation

Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Link: http://lkml.kernel.org/r/20200214204741.94112-14-jbi.octave@gmail.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>