ASoC: TWL6040: use of kzalloc/kfree requires the include of slab.h

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/soc/codecs/twl6040.c

@@ -27,6 +27,7 @@
 #include <linux/i2c.h>
 #include <linux/gpio.h>
 #include <linux/platform_device.h>
+#include <linux/slab.h>
 #include <linux/i2c/twl.h>
 
 #include <sound/core.h>