fix a agpgart_be.c compile warning

I got the following compile warning in 2.4.25-pre8:

<-- snip -->

...
gcc -D__KERNEL__
-I/home/bunk/linux/kernel-2.4/linux-2.4.25-pre8-full/include -Wall -Wstrict-prototypes -Wno-trigraphs -O2 -fno-strict-aliasing -fno-common -fomit-frame-pointer -pipe -mpreferred-stack-boundary=2 -march=k6
-nostdinc -iwithprefix include -DKBUILD_BASENAME=agpgart_be -c -o agpgart_be.o
agpgart_be.c
...
agpgart_be.c:5647:17: warning: extra tokens at end of #undef directive
...

<-- snip -->

The following patch fixes this issue:

@@ -5644,7 +5644,7 @@
 #define GET_PAGE_DIR_IDX(addr) (GET_PAGE_DIR_OFF(addr) - \
 	GET_PAGE_DIR_OFF(agp_bridge.gart_bus_addr))
 #define GET_GATT_OFF(addr) ((addr & 0x003ff000) >> 12)
-#undef  GET_GATT(addr)
+#undef  GET_GATT
 #define GET_GATT(addr) (ati_generic_private.gatt_pages[\
 	GET_PAGE_DIR_IDX(addr)]->remapped)
 

Please apply
Adrian

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed