KVM: X86: Rename variable smap to not_smap in permission_fault()

Comments above the variable says the bit is set when SMAP is overridden
or the same meaning in update_permission_bitmask(): it is not subjected
to SMAP restriction.

Renaming it to reflect the negative implication and make the code better
readability.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Message-Id: <20220311070346.45023-4-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>