f2fs: fix typo

Fix typo and some grammatical errors.

The words "filesystem" and "readahead" are being used without the space treewide.

Signed-off-by: Park Ju Hyung <qkrwngud825@gmail.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 208f1a9..87cdac4 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -288,7 +288,7 @@
 		if (err && err != -ENOENT) {
 			goto fail;
 		} else if (err == -ENOENT) {
-			/* direct node is not exist */
+			/* direct node does not exists */
 			if (whence == SEEK_DATA) {
 				pgofs = PGOFS_OF_NEXT_DNODE(pgofs,
 							F2FS_I(inode));