Fix another thinko in peeling for gap compute of get_group_load_store_type

Fix another thinko in peeling for gap compute of get_group_load_store_type

There's inconsistent handling of the cpart_size == cnunits which
currently avoids reporting peeling for gaps being insufficient, but
the following condition which is enough to trigger it,
cremain + group_size < cpart_size with cpart_size == cnunits is
equal to the condition that brings us here in the first place,
maybe_lt (remain + group_size, nunits).  The following fixes this
by not checking cpart_size against special values.

	* tree-vect-stmts.cc (get_group_load_store_type): Do not
	exempt cpart_size == cnunits from failing.