staging: vchip_shim: Remove unneeded stddef.h include

Building on openrisc musl toolchain this causes the allyesconfig build
to fail.

  drivers/staging/vc04_services/interface/vchiq_arm/vchiq_shim.c:42:20:
  fatal error: stddef.h: No such file or directory

Removing this causes no issues with the build.
Signed-off-by: Stafford Horne <shorne@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_shim.c

@@ -39,8 +39,6 @@
 
 #include "vchiq_util.h"
 
-#include <stddef.h>
-
 #define vchiq_status_to_vchi(status) ((int32_t)status)
 
 typedef struct {