block/file-posix: Remove redundant statement in raw_handle_perm_lock()

Clang static code analyzer show warning:
  block/file-posix.c:891:9: warning: Value stored to 'op' is never read
        op = RAW_PL_ABORT;
        ^    ~~~~~~~~~~~~

Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Chen Qun <kuhn.chenqun@huawei.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20200302130715.29440-5-kuhn.chenqun@huawei.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>