staging: goldfish: audio: fix compiliation on arm

We do actually need slab.h, by luck we get it on other platforms but not
always on ARM. Include it properly.

Signed-off-by: Greg Hackmann <[e-mail]>
Signed-off-by: Jin Qian <[e-mail]>
Signed-off-by: Alan <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/goldfish/goldfish_audio.c

···
 #include <linux/sched.h>
 #include <linux/dma-mapping.h>
 #include <linux/uaccess.h>
+#include <linux/slab.h>
 #include <linux/goldfish.h>
 
 MODULE_AUTHOR("Google, Inc.");