ext4: Fix building with EXT4FS_DEBUG

When bg_free_blocks_count was renamed to bg_free_blocks_count_lo in
560671a0, its uses under EXT4FS_DEBUG were not changed to the helper
ext4_free_blks_count.

Another commit, 498e5f24, also did not change everything needed under
EXT4FS_DEBUG, thus making it spill some warnings related to printing
format.

This commit fixes both issues and makes ext4 build again when
EXT4FS_DEBUG is enabled.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 918aec0..deba54f 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -3025,7 +3025,7 @@
 		goto out_err;
 
 	ext4_debug("using block group %u(%d)\n", ac->ac_b_ex.fe_group,
-			gdp->bg_free_blocks_count);
+			ext4_free_blks_count(sb, gdp));
 
 	err = ext4_journal_get_write_access(handle, gdp_bh);
 	if (err)