[X86] Fix assert fails in pass X86AvoidSFBPass

Fixes https://bugs.llvm.org/show_bug.cgi?id=38743

The function removeRedundantBlockingStores is supposed to remove any blocking stores contained in each other in lockingStoresDispSizeMap.
But it currently looks only at the previous one, which will miss some cases that result in assert.

This patch refine the function to check all previous layouts until find the uncontained one. So all redundant stores will be removed.

Patch by Pengfei Wang

Differential Revision: https://reviews.llvm.org/D55642

llvm-svn: 349660