fix AGP warning

drivers/char/agp/intel-agp.c: In function 'intel_i965_g33_setup_chipset_flush':
drivers/char/agp/intel-agp.c:872: warning: right shift count >= width of type

I wish the agp code wasn't written in a 10,000-column xterm :(

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dave Airlie <airlied@linux.ie>