drm/amd/amdgpu : Fix NULL pointer comparison

Replace direct comparisons to NULL i.e.
'x == NULL' with '!x'. As per coding standard.
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NRavikant B Sharma <ravikant.s2@samsung.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

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

@@ -70,7 +70,7 @@ static bool igp_read_bios_from_vram(struct amdgpu_device *adev)
 		return false;
 	}
 	adev->bios = kmalloc(size, GFP_KERNEL);
-	if (adev->bios == NULL) {
+	if (!adev->bios) {
 		iounmap(bios);
 		return false;
 	}

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

@@ -327,9 +327,8 @@ int amdgpu_sa_bo_new(struct amdgpu_sa_manager *sa_manager,
 		return -EINVAL;
 
 	*sa_bo = kmalloc(sizeof(struct amdgpu_sa_bo), GFP_KERNEL);
-	if ((*sa_bo) == NULL) {
+	if (!(*sa_bo))
 		return -ENOMEM;
-	}
 	(*sa_bo)->manager = sa_manager;
 	(*sa_bo)->fence = NULL;
 	INIT_LIST_HEAD(&(*sa_bo)->olist);

drivers/gpu/drm/amd/amdgpu/gfx_v8_0.c

@@ -3904,7 +3904,7 @@ static int gfx_v8_0_init_save_restore_list(struct amdgpu_device *adev)
 	int list_size;
 	unsigned int *register_list_format =
 		kmalloc(adev->gfx.rlc.reg_list_format_size_bytes, GFP_KERNEL);
-	if (register_list_format == NULL)
+	if (!register_list_format)
 		return -ENOMEM;
 	memcpy(register_list_format, adev->gfx.rlc.register_list_format,
 			adev->gfx.rlc.reg_list_format_size_bytes);