Fix optimize_mask_stores profile update

Fix optimize_mask_stores profile update

While looking into sphinx3 regression I noticed that vectorizer produces
BBs with overall probability count 120%.  This patch fixes it.
Richi, I don't know how to create a testcase, but having one would
be nice.

Bootstrapped/regtested x86_64-linux, will commit it shortly.

gcc/ChangeLog:

	PR tree-optimization/110649
	* tree-vect-loop.cc (optimize_mask_stores): Set correctly
	probability of the if-then-else construct.