f2fs: clean up with is_valid_blkaddr()

- rename is_valid_blkaddr() to is_valid_meta_blkaddr() for readability.
- introduce is_valid_blkaddr() for cleanup.

No logic change in this patch.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/inode.c

@@ -72,7 +72,7 @@ static bool __written_first_block(struct f2fs_inode *ri)
 {
 	block_t addr = le32_to_cpu(ri->i_addr[offset_in_addr(ri)]);
 
-	if (addr != NEW_ADDR && addr != NULL_ADDR)
+	if (is_valid_blkaddr(addr))
 		return true;
 	return false;
 }