hw/block/nvme: fix the nsid 'invalid' value

The `nvme_nsid()` function returns '-1' (FFFFFFFFh) when the given
namespace is NULL. Since FFFFFFFFh is actually a valid namespace
identifier (the "broadcast" value), change this to be '0' since that
actually *is* the invalid value.

Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
Reviewed-by: Gollu Appalanaidu <anaidu.gollu@samsung.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>

hw/block/nvme-ns.h

@@ -96,7 +96,7 @@ static inline uint32_t nvme_nsid(NvmeNamespace *ns)
         return ns->params.nsid;
     }
 
-    return -1;
+    return 0;
 }
 
 static inline bool nvme_ns_shared(NvmeNamespace *ns)