winex11.drv: Cast-qual warnings fix (2 of 3)

[Andrew Talbot]

Changelog:
    winex11.drv: Cast-qual warnings fix.

diff -urN a/dlls/winex11.drv/opengl.c b/dlls/winex11.drv/opengl.c
--- a/dlls/winex11.drv/opengl.c	2006-11-13 17:34:40.000000000 +0000
+++ b/dlls/winex11.drv/opengl.c	2006-11-25 17:57:30.000000000 +0000
@@ -332,7 +332,7 @@
         return FALSE;
     }
 
-#define LOAD_FUNCPTR(f) if((p##f = (void*)pglXGetProcAddressARB((unsigned char*)#f)) == NULL) goto sym_not_found;
+#define LOAD_FUNCPTR(f) if((p##f = (void*)pglXGetProcAddressARB((const unsigned char*)#f)) == NULL) goto sym_not_found;
 /* GLX 1.0 */
 LOAD_FUNCPTR(glXChooseVisual)
 LOAD_FUNCPTR(glXCreateContext)
@@ -1353,7 +1353,7 @@
     /* Check the table of WGL extensions to see if we need to return a WGL extension
      * or a function pointer to a native OpenGL function. */
     if(strncmp(lpszProc, "wgl", 3) != 0) {
-        return pglXGetProcAddressARB((GLubyte*)lpszProc);
+        return pglXGetProcAddressARB((const GLubyte*)lpszProc);
     } else {
         TRACE("('%s'):%*s", lpszProc, padding, " ");
         for (i = 0; i < WineGLExtensionListSize; ++i) {