drm/amdgpu: fix potential NULL pointer when check_atom_bios() fails

Asic funcs pointer needs being checked whether is NULL. Because when
check_atom_bios() fails in req_init_data handshake, asic funcs pointer
is not initialized yet.
Signed-off-by: Jiawei Gu <Jiawei.Gu@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -155,7 +155,7 @@ static bool amdgpu_read_bios_from_rom(struct amdgpu_device *adev)
 	u8 header[AMD_VBIOS_SIGNATURE_END+1] = {0};
 	int len;
 
-	if (!adev->asic_funcs->read_bios_from_rom)
+	if (!adev->asic_funcs || !adev->asic_funcs->read_bios_from_rom)
 		return false;
 
 	/* validate VBIOS signature */
@@ -348,7 +348,8 @@ static bool amdgpu_read_disabled_bios(struct amdgpu_device *adev)
 	if (adev->flags & AMD_IS_APU)
 		return igp_read_bios_from_vram(adev);
 	else
-		return amdgpu_asic_read_disabled_bios(adev);
+		return (!adev->asic_funcs || !adev->asic_funcs->read_disabled_bios) ?
+			false : amdgpu_asic_read_disabled_bios(adev);
 }
 
 #ifdef CONFIG_ACPI