drm: have config DRM_WERROR depend on !WERROR

If WERROR is already enabled, there's no point in enabling DRM_WERROR or
asking users about it.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Closes: https://lore.kernel.org/r/CAHk-=whxT8D_0j=bjtrvj-O=VEOjn6GW8GK4j2V+BiDUntZKAQ@mail.gmail.com
Fixes: f89632a9 ("drm: Add CONFIG_DRM_WERROR")
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240516083343.1375687-1-jani.nikula@intel.comSigned-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/Kconfig

@@ -450,6 +450,7 @@ config DRM_PRIVACY_SCREEN
 config DRM_WERROR
 	bool "Compile the drm subsystem with warnings as errors"
 	depends on DRM && EXPERT
+	depends on !WERROR
 	default n
 	help
 	  A kernel build should not cause any compiler warnings, and this