drm/i2c/sil164: use drm_debug_enabled() to check for debug categories

Allow better abstraction of the drm_debug global variable in the
future. No functional changes.

Cc: Francisco Jerez <[e-mail]>
Reviewed-by: Francisco Jerez <[e-mail]>
Signed-off-by: Jani Nikula <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/f6f[e-mail]

drivers/gpu/drm/i2c/sil164_drv.c

···
 	((struct sil164_priv *)to_encoder_slave(x)->slave_priv)
 
 #define sil164_dbg(client, format, ...) do {				\
-		if (drm_debug & DRM_UT_KMS)				\
+		if (drm_debug_enabled(DRM_UT_KMS))			\
 			dev_printk(KERN_DEBUG, &client->dev,		\
 				   "%s: " format, __func__, ## __VA_ARGS__); \
 	} while (0)