When 'iio_dev_opaque->buffer_ioctl_handler' alloc fails in
iio_buffers_alloc_sysfs_and_mask(), the 'attrs' allocated in
iio_buffer_register_legacy_sysfs_groups() will be leaked:

unreferenced object 0xffff888108568d00 (size 128):
  comm "88", pid 2014, jiffies 4294963294 (age 26.920s)
  hex dump (first 32 bytes):
    80 3e da 02 80 88 ff ff 00 3a da 02 80 88 ff ff  .>.......:......
    00 35 da 02 80 88 ff ff 00 38 da 02 80 88 ff ff  .5.......8......
  backtrace:
    [<0000000095a9e51e>] __kmalloc+0x1a3/0x2f0
    [<00000000faa3735e>] iio_buffers_alloc_sysfs_and_mask+0xfa3/0x1480 [industrialio]
    [<00000000a46384dc>] __iio_device_register+0x52e/0x1b40 [industrialio]
    [<00000000210af05e>] __devm_iio_device_register+0x22/0x80 [industrialio]
    [<00000000730d7b41>] adjd_s311_probe+0x195/0x200 [adjd_s311]
    [<00000000c0f70eb9>] i2c_device_probe+0xa07/0xbb0

The iio_buffer_register_legacy_sysfs_groups() is
called in __iio_buffer_alloc_sysfs_and_mask(),
so move the iio_buffer_unregister_legacy_sysfs_groups()
into __iio_buffer_free_sysfs_and_mask(), then the memory
will be freed.
Reported-by: Hulk Robot <hulkci@huawei.com>
Fixes: d9a62574 ("iio: core: merge buffer/ & scan_elements/ attributes")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20211018063718.1971240-1-yangyingliang@huawei.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>