mkfs: relax size check

Number of total data blocks in filesystem reported by statfs
may be less than current formula of 90%. For example ext4 will
subtract "s_first_data_block plus internal journal blocks".

With recent change to e2fsprogs, overhead calculated in user-space
increased slightly and LTP test started failing:
  tytso/e2fsprogs@59037c5

Since there's no strict rule how much the overhead will be,
as rule of thumb relax the condition to 80%.

Signed-off-by: Jan Stancek <jstancek@redhat.com>
Reviewed-by: Petr Vorel <pvorel@suse.cz>
Reviewed-by: Li Wang <liwang@redhat.com>

testcases/commands/mkfs/mkfs01.sh

@@ -69,11 +69,11 @@ mkfs_verify_size()
 	# 1k-block size should be devided by this argument for ntfs verification.
 	if [ "$1" = "ntfs" ]; then
 		local rate=1024/512
-		if [ $blocknum -lt "$(($2/$rate*9/10))" ]; then
+		if [ $blocknum -lt "$(($2/$rate*8/10))" ]; then
 			return 1
 		fi
 	else
-		if [ $blocknum -lt "$(($2*9/10))" ]; then
+		if [ $blocknum -lt "$(($2*8/10))" ]; then
 			return 1
 		fi
 	fi