i965/miptree: Fix comments for map mode

The comment for intel_miptree_map::mode claimed that it was a bitmask of
GL_MAP_{READ,WRITE,INVALIDATE}_BIT. In reality, the bitmask may include
any of {GL,BRW}_MAP_*_BIT.

Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>
Acked-by: Ben Widawsky <benjamin.widawsky@intel.com>

src/mesa/drivers/dri/i965/intel_mipmap_tree.h

@@ -75,7 +75,7 @@ struct intel_texture_image;
 #define BRW_MAP_DIRECT_BIT	0x80000000
 
 struct intel_miptree_map {
-   /** Bitfield of GL_MAP_READ_BIT, GL_MAP_WRITE_BIT, GL_MAP_INVALIDATE_BIT */
+   /** Bitfield of GL_MAP_*_BIT and BRW_MAP_*_BIT. */
    GLbitfield mode;
    /** Region of interest for the map. */
    int x, y, w, h;