drm/print: Handle NULL drm device in __drm_printk()

drm_{err,warn,...}() use __drm_printk() which takes a drm device pointer and
uses the embedded device pointer to print the device. This facility handles
NULL device pointer, but not NULL drm device pointer. This patch makes
__drm_printk() also handle a NULL drm device pointer. The printed output is
identical to if drm->dev had been NULL.

Signed-off-by: Luben Tuikov <[e-mail]>
Reviewed-by: Jani Nikula <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

include/drm/drm_print.h

···
 
 /* Helper for struct drm_device based logging. */
 #define __drm_printk(drm, level, type, fmt, ...)			\
-	dev_##level##type((drm)->dev, "[drm] " fmt, ##__VA_ARGS__)
+	dev_##level##type((drm) ? (drm)->dev : NULL, "[drm] " fmt, ##__VA_ARGS__)
 
 
 #define drm_info(drm, fmt, ...)					\