KVM: selftests: Forcefully override ARCH from x86_64 to x86

KVM: selftests: Forcefully override ARCH from x86_64 to x86

commit 17e5a9b77716564540d81f0c1e6082d28cf305c9 upstream.

Forcefully override ARCH from x86_64 to x86 to handle the scenario where
the user specifies ARCH=x86_64 on the command line.

Fixes: 9af04539d474 ("KVM: selftests: Override ARCH for x86_64 instead of using ARCH_DIR")
Cc: stable@vger.kernel.org
Reported-by: David Matlack <dmatlack@google.com>
Closes: https://lore.kernel.org/all/20250724213130.3374922-1-dmatlack@google.com
Link: https://lore.kernel.org/r/20251007223057.368082-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>