radeon: r100: Silence 'may be used uninitialized' warnings

  CC [M]  drivers/gpu/drm/radeon/r100.o
In file included from drivers/gpu/drm/radeon/radeon_mode.h:37:0,
                 from drivers/gpu/drm/radeon/radeon.h:80,
                 from drivers/gpu/drm/radeon/r100.c:33:
drivers/gpu/drm/radeon/r100.c: In function 'r100_bandwidth_update':
include/drm/drm_fixed.h:64:13: warning: 'crit_point_ff.full' may be used uninitialized in this function [-Wmaybe-uninitialized]
  u64 tmp = ((u64)A.full << 13);
             ^
drivers/gpu/drm/radeon/r100.c:3153:63: note: 'crit_point_ff.full' was declared here
  fixed20_12 peak_disp_bw, mem_bw, pix_clk, pix_clk2, temp_ff, crit_point_ff;
                                                               ^
drivers/gpu/drm/radeon/r100.c:3583:42: warning: 'disp_drain_rate.full' may be used uninitialized in this function [-Wmaybe-uninitialized]
     temp_ff.full = read_return_rate.full - disp_drain_rate.full;

gcc version 5.3.1 20151219 (Ubuntu 5.3.1-4ubuntu1)

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <airlied@linux.ie>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>