KVM: VMX: Use named operands in inline asm

Convert the non-asm-goto version of the inline asm in __vmcs_readl() to
use named operands, similar to its asm-goto version.

Do this in preparation of changing the ASM_CALL_CONSTRAINT primitive.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Sean Christopherson <seanjc@google.com>
Cc: linux-kernel@vger.kernel.org