drm/amd/include/navi10_ip_offset: Mark top-level IP_BASE as __maybe_unused

Fixes the following W=1 kernel build warning(s):

In file included from drivers/gpu/drm/amd/amdgpu/navi10_reg_init.c:27:
drivers/gpu/drm/amd/amdgpu/../include/navi10_ip_offset.h:127:29: warning: ‘UMC_BASE’ defined but not used [-Wunused-const-variable=]
127 | static const struct IP_BASE UMC_BASE ={ { { { 0x00014000, 0, 0, 0, 0, 0 } },
| ^~~~~~~~
drivers/gpu/drm/amd/amdgpu/../include/navi10_ip_offset.h:109:29: warning: ‘RSMU_BASE’ defined but not used [-Wunused-const-variable=]
109 | static const struct IP_BASE RSMU_BASE = { { { { 0x00012000, 0, 0, 0, 0, 0 } },
| ^~~~~~~~~
drivers/gpu/drm/amd/amdgpu/../include/navi10_ip_offset.h:61:29: warning: ‘FUSE_BASE’ defined but not used [-Wunused-const-variable=]
61 | static const struct IP_BASE FUSE_BASE ={ { { { 0x00017400, 0, 0, 0, 0, 0 } },
| ^~~~~~~~~

Acked-by: Christian König <[e-mail]>
Cc: Alex Deucher <[e-mail]>
Cc: "Christian König" <[e-mail]>
Cc: David Airlie <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Lee Jones <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/include/navi10_ip_offset.h

···
  
 struct IP_BASE {
 	struct IP_BASE_INSTANCE instance[MAX_INSTANCE];
-};
+} __maybe_unused;
 
 
 static const struct IP_BASE ATHUB_BASE            ={ { { { 0x00000C00, 0, 0, 0, 0, 0 } },