fbdev: potential information leak in do_fb_ioctl()

fbdev: potential information leak in do_fb_ioctl()

The "fix" struct has a 2 byte hole after ->ywrapstep and the
"fix = info->fix;" assignment doesn't necessarily clear it.  It depends
on the compiler.  The solution is just to replace the assignment with an
memcpy().

Fixes: 1f5e31d7e55a ("fbmem: don't call copy_from/to_user() with mutex held")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Andrea Righi <righi.andrea@gmail.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Peter Rosin <peda@axentia.se>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200113100132.ixpaymordi24n3av@kili.mountain