ASoC: rt5514: Remove superfluous linux/kthread.h inclusion

It's nowhere used in this driver code.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/rt5514-spi.c

@@ -20,7 +20,6 @@
 #include <linux/slab.h>
 #include <linux/gpio.h>
 #include <linux/sched.h>
-#include <linux/kthread.h>
 #include <linux/uaccess.h>
 #include <linux/miscdevice.h>
 #include <linux/regulator/consumer.h>