KVM: arm64: Stop clobbering x0 for HVC_SOFT_RESTART

KVM: arm64: Stop clobbering x0 for HVC_SOFT_RESTART

commit b9e10d4a6c9f5cbe6369ce2c17ebc67d2e5a4be5 upstream.

HVC_SOFT_RESTART is given values for x0-2 that it should installed
before exiting to the new address so should not set x0 to stub HVC
success or failure code.

Fixes: af42f20480bf1 ("arm64: hyp-stub: Zero x0 on successful stub handling")
Cc: stable@vger.kernel.org
Signed-off-by: Andrew Scull <ascull@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200706095259.1338221-1-ascull@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>