ext4: fix memory leak in parse_apply_sb_mount_options()

In the Linux kernel, the following vulnerability has been resolved:

ext4: fix memory leak in parse_apply_sb_mount_options()

If processing the on-disk mount options fails after any memory was

allocated in the ext4_fs_context, e.g. s_qf_names, then this memory is

leaked. Fix this by calling ext4_fc_free() instead of kfree() directly.

Reproducer:

mkfs.ext4 -F /dev/vdc

tune2fs /dev/vdc -E mount_opts=usrjquota=file

echo clear > /sys/kernel/debug/kmemleak

mount /dev/vdc /vdc

echo scan > /sys/kernel/debug/kmemleak

sleep 5

echo scan > /sys/kernel/debug/kmemleak

cat /sys/kernel/debug/kmemleak