hw/9pfs/9p-synth: Replaced qemu_mutex_lock with QEMU_LOCK_GUARD

Replaced a call to qemu_mutex_lock and its respective call to
qemu_mutex_unlock and used QEMU_LOCK_GUARD macro in their place.
This simplifies the code by removing the call required to unlock
and also eliminates goto paths.

Signed-off-by: Mahmoud Mandour <ma.mandourr@gmail.com>
Acked-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Message-Id: <20210311031538.5325-9-ma.mandourr@gmail.com>
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>

hw/9pfs/9p-synth.c

@@ -79,11 +79,11 @@ int qemu_v9fs_synth_mkdir(V9fsSynthNode *parent, int mode,
     if (!parent) {
         parent = &synth_root;
     }
-    qemu_mutex_lock(&synth_mutex);
+    QEMU_LOCK_GUARD(&synth_mutex);
     QLIST_FOREACH(tmp, &parent->child, sibling) {
         if (!strcmp(tmp->name, name)) {
             ret = EEXIST;
-            goto err_out;
+            return ret;
         }
     }
     /* Add the name */
@@ -94,8 +94,6 @@ int qemu_v9fs_synth_mkdir(V9fsSynthNode *parent, int mode,
                       node->attr, node->attr->inode);
     *result = node;
     ret = 0;
-err_out:
-    qemu_mutex_unlock(&synth_mutex);
     return ret;
 }
 
@@ -116,11 +114,11 @@ int qemu_v9fs_synth_add_file(V9fsSynthNode *parent, int mode,
         parent = &synth_root;
     }
 
-    qemu_mutex_lock(&synth_mutex);
+    QEMU_LOCK_GUARD(&synth_mutex);
     QLIST_FOREACH(tmp, &parent->child, sibling) {
         if (!strcmp(tmp->name, name)) {
             ret = EEXIST;
-            goto err_out;
+            return ret;
         }
     }
     /* Add file type and remove write bits */
@@ -136,8 +134,6 @@ int qemu_v9fs_synth_add_file(V9fsSynthNode *parent, int mode,
     pstrcpy(node->name, sizeof(node->name), name);
     QLIST_INSERT_HEAD_RCU(&parent->child, node, sibling);
     ret = 0;
-err_out:
-    qemu_mutex_unlock(&synth_mutex);
     return ret;
 }