vect: Don't pass subtype to vect_widened_op_tree where not needed [PR 110142]

This patch fixes an issue introduced by
g:2f482a07, where a subtype was beeing passed
to vect_widened_op_tree, when no subtype was to be used. This lead to an
errorneous use of IFN_VEC_WIDEN_MINUS.

gcc/ChangeLog:

	PR middle-end/110142
	* tree-vect-patterns.cc (vect_recog_widen_op_pattern): Don't pass
	subtype to vect_widened_op_tree and remove subtype parameter, also
	remove superfluous overloaded function definition.
	(vect_recog_widen_plus_pattern): Remove subtype parameter and dont pass
	to call to vect_recog_widen_op_pattern.
	(vect_recog_widen_minus_pattern): Likewise.

gcc/testsuite/ChangeLog:

	* gcc.dg/vect/pr110142.c: New test.