x86/hvm: Fix Misra Rule 19.1 regression

x86/hvm: Fix Misra Rule 19.1 regression

Despite noticing an impending Rule 19.1 violation, the adjustment made (the
uint32_t cast) wasn't sufficient to avoid it.  Try again.

Subsequently noticed by Coverity too.

Fixes: 6a98383b0877 ("x86/HVM: clear upper halves of GPRs upon entry from 32-bit code")
Coverity-IDs: 1596289 thru 1596298
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
master commit: d0a718a45f14b86471d8eb3083acd72760963470
master date: 2024-04-11 13:23:08 +0100