iio: buffer: move __iio_buffer_free_sysfs_and_mask() before alloc

iio: buffer: move __iio_buffer_free_sysfs_and_mask() before alloc

The __iio_buffer_free_sysfs_and_mask() function will be used in
iio_buffer_alloc_sysfs_and_mask() when multiple buffers will be attached to
the IIO device.
This will need to be used to cleanup resources on each buffer, when the
buffers cleanup unwind will occur on the error path.

The move is done in this patch to make the patch that adds multiple buffers
per IIO device a bit cleaner.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20210215104043.91251-18-alexandru.ardelean@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>