nvme: Fix uninitialized-variable warning

gcc may detect a false positive on nvme using an unintialized variable
if setting features fails. Since this is not a fast path, explicitly
initialize this variable to suppress the warning.
Reported-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>

drivers/nvme/host/core.c

@@ -1165,8 +1165,8 @@ static int nvme_identify_ns(struct nvme_ctrl *ctrl,
 static int nvme_features(struct nvme_ctrl *dev, u8 op, unsigned int fid,
 		unsigned int dword11, void *buffer, size_t buflen, u32 *result)
 {
+	union nvme_result res = { 0 };
 	struct nvme_command c;
-	union nvme_result res;
 	int ret;
 
 	memset(&c, 0, sizeof(c));