f2fs: merge equivalent flags F2FS_GET_BLOCK_[READ|DIO]

Currently, the two flags F2FS_GET_BLOCK_[READ|DIO] are totally equivalent
and can be used interchangably in all scenarios they are involved in.
Neither of the flags is referenced in f2fs_map_blocks(), making them both
the default case. To remove the ambiguity, this patch merges both flags
into F2FS_GET_BLOCK_DEFAULT, and introduces an enum for all distinct flags.

Signed-off-by: Qiuyang Sun <sunqiuyang@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index e2b33b8..3eebd49 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -2074,7 +2074,7 @@
 	 */
 	while (map.m_lblk < pg_end) {
 		map.m_len = pg_end - map.m_lblk;
-		err = f2fs_map_blocks(inode, &map, 0, F2FS_GET_BLOCK_READ);
+		err = f2fs_map_blocks(inode, &map, 0, F2FS_GET_BLOCK_DEFAULT);
 		if (err)
 			goto out;
 
@@ -2116,7 +2116,7 @@
 
 do_map:
 		map.m_len = pg_end - map.m_lblk;
-		err = f2fs_map_blocks(inode, &map, 0, F2FS_GET_BLOCK_READ);
+		err = f2fs_map_blocks(inode, &map, 0, F2FS_GET_BLOCK_DEFAULT);
 		if (err)
 			goto clear_out;