drm/amdgpu: Fix clang warning: unused label 'exit'

Problem:
drivers/gpu/drm/amd/amdgpu/amdgpu_device.c:332:1: warning: unused label 'exit' [-Wunused-label]
exit:
^~~~~

Fix: Put #ifdef CONFIG_64BIT around exit
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210525184431.1170373-1-andrey.grodzovsky@amd.com

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c

@@ -330,7 +330,9 @@ void amdgpu_device_vram_access(struct amdgpu_device *adev, loff_t pos,
 	}
 	spin_unlock_irqrestore(&adev->mmio_idx_lock, flags);
 
+#ifdef CONFIG_64BIT
 exit:
+#endif
 	drm_dev_exit(idx);
 }