drm/radeon: Fix warning using plain integer as NULL

sparse static analysis tools generate a warning with this message
"Using plain integer as NULL pointer". In this case this warning is
being shown because we are trying to intialize a pointer to NULL using
integer value 0.
Signed-off-by: Abhinav Singh <singhabhinav9051571833@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/clearstate_evergreen.h

@@ -1049,7 +1049,7 @@ static const struct cs_extent_def SECT_CONTEXT_defs[] =
     {SECT_CONTEXT_def_5, 0x0000a29e, 5 },
     {SECT_CONTEXT_def_6, 0x0000a2a5, 56 },
     {SECT_CONTEXT_def_7, 0x0000a2de, 290 },
-    { 0, 0, 0 }
+    { NULL, 0, 0 }
 };
 static const u32 SECT_CLEAR_def_1[] =
 {
@@ -1060,7 +1060,7 @@ static const u32 SECT_CLEAR_def_1[] =
 static const struct cs_extent_def SECT_CLEAR_defs[] =
 {
     {SECT_CLEAR_def_1, 0x0000ffc0, 3 },
-    { 0, 0, 0 }
+    { NULL, 0, 0 }
 };
 static const u32 SECT_CTRLCONST_def_1[] =
 {
@@ -1070,11 +1070,11 @@ static const u32 SECT_CTRLCONST_def_1[] =
 static const struct cs_extent_def SECT_CTRLCONST_defs[] =
 {
     {SECT_CTRLCONST_def_1, 0x0000f3fc, 2 },
-    { 0, 0, 0 }
+    { NULL, 0, 0 }
 };
 static const struct cs_section_def evergreen_cs_data[] = {
     { SECT_CONTEXT_defs, SECT_CONTEXT },
     { SECT_CLEAR_defs, SECT_CLEAR },
     { SECT_CTRLCONST_defs, SECT_CTRLCONST },
-    { 0, SECT_NONE }
+    { NULL, SECT_NONE }
 };