drm/amd/amdgpu: Fix compiler warning in df driver

drm/amd/amdgpu: Fix compiler warning in df driver

Fix this warning:

  CC [M]  drivers/gpu/drm/amd/amdgpu/gfxhub_v1_1.o
In file included from drivers/gpu/drm/amd/amdgpu/amdgpu_ring.h:29,
                 from drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.h:26,
                 from drivers/gpu/drm/amd/amdgpu/amdgpu.h:43,
                 from drivers/gpu/drm/amd/amdgpu/df_v3_6.c:23:
drivers/gpu/drm/amd/amdgpu/df_v3_6.c: In function ‘df_v3_6_pmc_get_count’:
./include/drm/drm_print.h:487:2: warning: ‘hi_base_addr’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  487 |  __drm_dbg(DRM_UT_DRIVER, fmt, ##__VA_ARGS__)
      |  ^~~~~~~~~
drivers/gpu/drm/amd/amdgpu/df_v3_6.c:649:25: note: ‘hi_base_addr’ was declared here
  649 |  uint32_t lo_base_addr, hi_base_addr, lo_val = 0, hi_val = 0;
      |                         ^~~~~~~~~~~~
In file included from drivers/gpu/drm/amd/amdgpu/amdgpu_ring.h:29,
                 from drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.h:26,
                 from drivers/gpu/drm/amd/amdgpu/amdgpu.h:43,
                 from drivers/gpu/drm/amd/amdgpu/df_v3_6.c:23:
./include/drm/drm_print.h:487:2: warning: ‘lo_base_addr’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  487 |  __drm_dbg(DRM_UT_DRIVER, fmt, ##__VA_ARGS__)
      |  ^~~~~~~~~
drivers/gpu/drm/amd/amdgpu/df_v3_6.c:649:11: note: ‘lo_base_addr’ was declared here
  649 |  uint32_t lo_base_addr, hi_base_addr, lo_val = 0, hi_val = 0;

Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>