Don't cast the return value of malloc/realloc

This patch has been generated by the following Coccinelle semantic
patch:

// Don't cast the return value of malloc/realloc.
//
// Casting the return value of malloc/realloc only stands to hide
// errors.

@@
type T;
expression E1, E2;
@@
- (T)
(
_mesa_align_calloc(E1, E2)
|
_mesa_align_malloc(E1, E2)
|
calloc(E1, E2)
|
malloc(E1)
|
realloc(E1, E2)
)

src/glx/glx_pbuffer.c

@@ -326,7 +326,7 @@ GetDrawableAttribute(Display * dpy, GLXDrawable drawable,
    length = reply.length;
    if (length) {
       num_attributes = (use_glx_1_3) ? reply.numAttribs : length / 2;
-      data = (CARD32 *) malloc(length * sizeof(CARD32));
+      data = malloc(length * sizeof(CARD32));
       if (data == NULL) {
          /* Throw data on the floor */
          _XEatData(dpy, length);