x86/sev: Simplify the code by removing unnecessary 'else' statement

No need for an 'else' statement after a 'return'.

[ mingo: Clarified the changelog ]

Signed-off-by: Peng Hao <flyingpeng@tencent.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: linux-kernel@vger.kernel.org