x86_64: Fix wide argument increment

This patch fixes to always increment the index for a wide argument,
and fixes the index upper bound.
Otherwise, the mapping may be incorrect.

Change-Id: I0116d8fd0a0a5c1270a23129c73a9e3651132977
Signed-off-by: Chao-ying Fu <chao-ying.fu@intel.com>
Signed-off-by: Serguei Katkov <serguei.i.katkov@intel.com>