[SLP] Update X86/schedule_budget.ll test case to show budget impact

The comments and the checks in
  test/Transforms/SLPVectorizer/X86/schedule_budget.ll
did not match. After commit 352c46e7 the vectorization
has happened also with the reduced budget.

This patch is supposed to restore the original intention with the
test case (the one described in the comments). We want to see
that a restricted budget may reduce the amount of vectorization (i.e.
verifying that the -slp-schedule-budget option makes a difference),
while a higher budget still result in vectorization.

Differential Revision: https://reviews.llvm.org/D152530