block/vvfat.c fix leak when failure occurs

block/vvfat.c fix leak when failure occurs

Function vvfat_open called function enable_write_target and init_directories,
and these functions malloc new memory for BDRVVVFATState::qcow_filename,
BDRVVVFATState::used_clusters, and BDRVVVFATState::cluster_buff.

When the specified folder does not exist ,it may contains memory leak.
After init_directories function is executed, the vvfat_open return -EIO,
and bdrv_open_driver goto label open_failed,
the program use g_free(bs->opaque) to release BDRVVVFATState struct
without members mentioned.

command line:
qemu-system-x86_64 -hdb <vdisk qcow file>  -usb -device usb-storage,drive=fat16
-drive file=fat:rw:fat-type=16:"<path of a host folder does not exist>",
id=fat16,format=raw,if=none

enable_write_target called:
(gdb) bt
    at ../block/vvfat.c:3114
    flags=155650, errp=0x7fffffffd780) at ../block/vvfat.c:1236
    node_name=0x0, options=0x555556fa45d0, open_flags=155650,
    errp=0x7fffffffd890) at ../block.c:1558
    errp=0x7fffffffd890) at ../block.c:1852
    reference=0x0, options=0x555556fa45d0, flags=40962, parent=0x555556f98cd0,
    child_class=0x555556b1d6a0 <child_of_bds>, child_role=19,
    errp=0x7fffffffda90) at ../block.c:3779
    options=0x555556f9cfc0, bdref_key=0x555556239bb8 "file",
    parent=0x555556f98cd0, child_class=0x555556b1d6a0 <child_of_bds>,
    child_role=19, allow_none=true, errp=0x7fffffffda90) at ../block.c:3419
    reference=0x0, options=0x555556f9cfc0, flags=8194, parent=0x0,
    child_class=0x0, child_role=0, errp=0x555556c98c40 <error_fatal>)
    at ../block.c:3726
    options=0x555556f757b0, flags=0, errp=0x555556c98c40 <error_fatal>)
    at ../block.c:3872
    options=0x555556f757b0, flags=0, errp=0x555556c98c40 <error_fatal>)
    at ../block/block-backend.c:436
    bs_opts=0x555556f757b0, errp=0x555556c98c40 <error_fatal>)
    at ../blockdev.c:608
    errp=0x555556c98c40 <error_fatal>) at ../blockdev.c:992
......

Signed-off-by: Daniella Lee <daniellalee111@gmail.com>
Message-Id: <20211119112553.352222-1-daniellalee111@gmail.com>
[hreitz: Took commit message from v1]
Signed-off-by: Hanna Reitz <hreitz@redhat.com>