Use BUG_ON instead of a if condition followed by BUG.

Generated by: scripts/coccinelle/misc/bugon.cocci
Reviewed-by: NChristian König <christian.koenig@amd.com>
Reviewd-by: NXiangliang.Yu <Xiangliang.Yu@amd.com>
CC: Xiangliang Yu <Xiangliang.Yu@amd.com>
Signed-off-by: NJulia Lawall <julia.lawall@lip6.fr>
Signed-off-by: NFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>