meta: make mem_ctx non-global.

I can't see any external users, and this is a global symbol,

Reviewed-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

src/mesa/drivers/common/meta.c

@@ -78,7 +78,7 @@
 #include "main/glformats.h"
 #include "../glsl/ralloc.h"
 
-
+static void *mem_ctx;
 /** Return offset in bytes of the field within a vertex struct */
 #define OFFSET(FIELD) ((void *) offsetof(struct vertex, FIELD))
 

src/mesa/drivers/common/meta.h

@@ -58,8 +58,6 @@
 #define MESA_META_MULTISAMPLE          0x100000
 /**\}*/
 
-void *mem_ctx;
-
 extern void
 _mesa_meta_init(struct gl_context *ctx);