platform/olpc: Fix uninitialized data in debugfs write

[ Upstream commit 40ec787e1adf302c11668d4cc69838f4d584187d ]

The call to:

	size = simple_write_to_buffer(cmdbuf, sizeof(cmdbuf), ppos, buf, size);

will succeed if at least one byte is written to the "cmdbuf" buffer.
The "*ppos" value controls which byte is written.  Another problem is
that this code does not check for errors so it's possible for the entire
buffer to be uninitialized.

Inintialize the struct to zero to prevent reading uninitialized stack
data.

Debugfs is normally only writable by root so the impact of this bug is
very minimal.

Fixes: 6cca83d4 ("Platform: OLPC: move debugfs support from x86 EC driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/YthIKn+TfZSZMEcM@kili


Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>