iio: backend: make sure to NULL terminate stack buffer

iio: backend: make sure to NULL terminate stack buffer

[ Upstream commit 035b4989211dc1c8626e186d655ae8ca5141bb73 ]

Make sure to NULL terminate the buffer in
iio_backend_debugfs_write_reg() before passing it to sscanf(). It is a
stack variable so we should not assume it will 0 initialized.

Fixes: cdf01e0809a4 ("iio: backend: add debugFs interface")
Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20250218-dev-iio-misc-v1-1-bf72b20a1eb8@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>