x86/cpu: Fix LFENCE serialization check in init_amd()

The commit: 3f235279 ("x86/cpu: Restore AMD's DE_CFG MSR after resume")
which was backported from the upstream commit: 2632daebafd0 renamed the
MSR_F10H_DECFG_LFENCE_SERIALIZE macro to MSR_AMD64_DE_CFG_LFENCE_SERIALIZE.
The fix for 4.14 and 4.9 changed MSR_F10H_DECFG_LFENCE_SERIALIZE to
MSR_AMD64_DE_CFG_LFENCE_SERIALIZE_BIT in the init_amd() function, but should
have used MSR_AMD64_DE_CFG_LFENCE_SERIALIZE.  This causes a discrepency in the
LFENCE serialization check in the init_amd() function.

This causes a ~16% sysbench memory regression, when running:
    sysbench --test=memory run

Fixes: 3f235279 ("x86/cpu: Restore AMD's DE_CFG MSR after resume")
Signed-off-by: Rhythm Mahajan <rhythm.m.mahajan@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>