x86: rework of match_template()'s suffix checking

(Ab)using i386_opcode_modifier for this has been overkill, as the logic
doesn't really require the full structure. With the removal of
LONG_DOUBLE_MNEM_SUFFIX and No_ldSuf there's no good reason at all
anymore to pull out such a loop invariant: We're dealing a check of a
bit in the loop for a simple comparison. Do the original compares inside
the loop, thus also making it easier to understand what is actually
being checked.