drm/amdgpu/display: make a const array common_rates static, makes object smaller

Don't populate the const array common_rates on the stack but instead it
static. Makes the object code smaller by 80 bytes:

Before:
   text	   data	    bss	    dec	    hex	filename
 268019	  98322	    256	 366597	  59805	../display/amdgpu_dm/amdgpu_dm.o

After:
   text	   data	    bss	    dec	    hex	filename
 267843	  98418	    256	 366517	  597b5	../display/amdgpu_dm/amdgpu_dm.o

Reduction of 80 bytes

(gcc version 10.3.0)
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -7570,8 +7570,10 @@ static uint add_fs_modes(struct amdgpu_dm_connector *aconnector)
 	 * 60 	    - Commonly used
 	 * 48,72,96 - Multiples of 24
 	 */
-	const uint32_t common_rates[] = { 23976, 24000, 25000, 29970, 30000,
-					 48000, 50000, 60000, 72000, 96000 };
+	static const uint32_t common_rates[] = {
+		23976, 24000, 25000, 29970, 30000,
+		48000, 50000, 60000, 72000, 96000
+	};
 
 	/*
 	 * Find mode with highest refresh rate with the same resolution