drm: refactor call to request_module

This reduces the size of the stack frame when calling request_module().
Performing the sprintf before the call is not needed.

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Paul Menzel <paulepanter@users.sourceforge.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>