drm: Add missing static storage class specifier

Fixes the following sparse warning:
drivers/gpu/drm/drm_info.c:238:5:
warning: symbol 'drm_gem_one_name_info' was not declared. Should it be static?

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>