target/i386/sev: Use size_t for object sizes

target/i386/sev: Use size_t for object sizes

This code was using both uint32_t and uint64_t for len.
Consistently use size_t instead.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Link: https://lore.kernel.org/r/20240626194950.1725800-3-richard.henderson@linaro.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>