sheepdog: Fix error handling sd_create()

As a bdrv_create() method, sd_create() must set an error and return
negative errno on failure.  It prints the error instead of setting it
when connect_to_sdog() fails.  Fix that.

While there, return the value of connect_to_sdog() like we do
elsewhere, instead of -EIO.  No functional change, as
connect_to_sdog() returns no other error code.

Many more suspicious uses of error_report() and error_report_err()
remain in other functions.  Left for another day.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/sheepdog.c

@@ -1829,14 +1829,12 @@ static int sd_create(const char *filename, QemuOpts *opts,
     if (s->inode.block_size_shift == 0) {
         SheepdogVdiReq hdr;
         SheepdogClusterRsp *rsp = (SheepdogClusterRsp *)&hdr;
-        Error *local_err = NULL;
         int fd;
         unsigned int wlen = 0, rlen = 0;
 
-        fd = connect_to_sdog(s, &local_err);
+        fd = connect_to_sdog(s, errp);
         if (fd < 0) {
-            error_report_err(local_err);
-            ret = -EIO;
+            ret = fd;
             goto out;
         }