blobstore: don't realloc any memory under scan-build

Scan-build has a real issue with reallocs. The original
error from latest version of scan-build is rather complicated,
but it can be greatly simplified with the following change:

> diff --git a/lib/blob/blobstore.c b/lib/blob/blobstore.c
> index 7580c9dd2..6a594edf3 100644
> --- a/lib/blob/blobstore.c
> +++ b/lib/blob/blobstore.c
> @@ -1147,8 +1147,9 @@
> _spdk_blob_persist_clear_clusters_cpl(spdk_bs_sequence_t *seq, void *cb_arg, int
>         } else if (blob->active.num_clusters != blob->active.cluster_array_size) {
>                 tmp = realloc(blob->active.clusters, sizeof(uint64_t) * blob->active.num_clusters);
>                 assert(tmp != NULL);
> -               blob->active.clusters = tmp;
> -               blob->active.cluster_array_size = blob->active.num_clusters;
> +               ctx->blob->active.clusters = tmp;
> +               assert(ctx->blob->active.clusters[0] != 14213);
> +               ctx->blob->active.cluster_array_size = ctx->blob->active.num_clusters;
>         }
>
>         _spdk_blob_persist_complete(seq, ctx, bserrno);
> ```

Scan-build will then complain:

blobstore.c:1151:10: warning: Use of memory after it is freed
                assert(ctx->blob->active.clusters[0] != 14213);

Asserting blob == ctx->blob, blob->active.clusters == ctx->...,
or even tmp != blob->active.clusters doesn't work, so use the
last resort scan-build weapon - #ifdef __clang_analyzer__.

The realloc in this case is just down-sizing a buffer to
save some memory. For scan-build, just don't do it. This
finally silences all scan-build false positives.

Change-Id: Ib88ea145370f5035eedd2412e98ee61f96ad1915
Signed-off-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/462868


Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>