block/qcow2-bitmap: Remove unneeded variable assignment

block/qcow2-bitmap: Remove unneeded variable assignment

Fix warning reported by Clang static code analyzer:

    CC      block/qcow2-bitmap.o
  block/qcow2-bitmap.c:650:5: warning: Value stored to 'ret' is never read
      ret = -EINVAL;
      ^     ~~~~~~~

Fixes: 88ddffae8
Reported-by: Clang Static Analyzer
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200215161557.4077-2-philmd@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>