drm/amdgpu/gmc6: fix DMA mask from 44 to 40 bits

The DMA mask on SI parts is 40 bits not 44.  Copy
paste typo.

Fixes: 244511f ("drm/amdgpu: simplify and cleanup setting the dma mask")
Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1762
Acked-by: Christian König <christian.koenig@amd.com>
Tested-by: Paul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/gmc_v6_0.c

@@ -841,12 +841,12 @@ static int gmc_v6_0_sw_init(void *handle)
 
 	adev->gmc.mc_mask = 0xffffffffffULL;
 
-	r = dma_set_mask_and_coherent(adev->dev, DMA_BIT_MASK(44));
+	r = dma_set_mask_and_coherent(adev->dev, DMA_BIT_MASK(40));
 	if (r) {
 		dev_warn(adev->dev, "No suitable DMA available.\n");
 		return r;
 	}
-	adev->need_swiotlb = drm_need_swiotlb(44);
+	adev->need_swiotlb = drm_need_swiotlb(40);
 
 	r = gmc_v6_0_init_microcode(adev);
 	if (r) {