[NFC][LoopCacheAnalysis] Update test cases to make sure the outputs follow the right order

In this patch we change test cases from using "CHECK" to using
"CHECK-NEXT", which is to ensure the order of loops output by
loop cache analysis is correct. After D124725 we fixed the
non-deterministic output order hence we did not use "CHECK-DAG"
anymore, and now we should really use "CHECK-NEXT" to make sure
the loops in the output loop vector follow the right order.

Reviewed By: bmahjour, #loopoptwg

Differential Revision: https://reviews.llvm.org/D124984