virtiofs: Fix spelling mistakes

Fix some spelling mistakes in comments:
refernce  ==> reference
happnes  ==> happens
threhold  ==> threshold
splitted  ==> split
mached  ==> matched

Signed-off-by: Zheng Yongjun <zhengyongjun3@huawei.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
index ff99ab2..a005859 100644
--- a/fs/fuse/dax.c
+++ b/fs/fuse/dax.c
@@ -212,7 +212,7 @@
 	dmap->writable = writable;
 	if (!upgrade) {
 		/*
-		 * We don't take a refernce on inode. inode is valid right now
+		 * We don't take a reference on inode. inode is valid right now
 		 * and when inode is going away, cleanup logic should first
 		 * cleanup dmap entries.
 		 */
@@ -621,7 +621,7 @@
 	}
 
 	/*
-	 * If read beyond end of file happnes, fs code seems to return
+	 * If read beyond end of file happens, fs code seems to return
 	 * it as hole
 	 */
 iomap_hole:
@@ -1206,7 +1206,7 @@
 			 ret);
 	}
 
-	/* If number of free ranges are still below threhold, requeue */
+	/* If number of free ranges are still below threshold, requeue */
 	kick_dmap_free_worker(fcd, 1);
 }
 
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index b8d58aa..1c8f79b 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -91,7 +91,7 @@
 {
 	/*
 	 * lockess check of fc->connected is okay, because atomic_dec_and_test()
-	 * provides a memory barrier mached with the one in fuse_wait_aborted()
+	 * provides a memory barrier matched with the one in fuse_wait_aborted()
 	 * to ensure no wake-up is missed.
 	 */
 	if (atomic_dec_and_test(&fc->num_waiting) &&
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 3f6ba68..46ddc46 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -645,7 +645,7 @@
  * == bytes_transferred or rw == WRITE, the caller sets 'pos' to -1.
  *
  * An example:
- * User requested DIO read of 64K. It was splitted into two 32K fuse requests,
+ * User requested DIO read of 64K. It was split into two 32K fuse requests,
  * both submitted asynchronously. The first of them was ACKed by userspace as
  * fully completed (req->out.args[0].size == 32K) resulting in pos == -1. The
  * second request was ACKed as short, e.g. only 1K was read, resulting in