drm: make drm_dev_set_unique() not use a format string

drm: make drm_dev_set_unique() not use a format string

drm_dev_set_unique() uses a format string to define the unique name of a
device.  This feature is not used as currently all the calls to this
function either use "%s" as a format string or directly use
dev_name().

Even though this second kind of call does not introduce security
problems, because there cannot be "%" characters in dev_name() results,
gcc issues a warning when building with -Wformat-security flag
("warning: format string is not a string literal (potentially
insecure)").  This warning is useful to find real bugs like the one
fixed by commit 3958b79266b1 ("configfs: fix kernel infoleak through
user-controlled format string").  False positives which do not bring
an extra value make the work of finding real bugs harder.

Therefore remove the format-string feature from drm_dev_set_unique().

Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1449829228-4425-1-git-send-email-nicolas.iooss_linux@m4x.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>