This commit update coh check assertion to enable aggressive
prefetch miss req / store miss req merge. Previous wrong
assertion forbids store req from stoping a previous prefetch

For example, consider 2 reqs with the same p address fire in order:
1) A prefetch with alias bit 00 need to change coh state from N->T
2) A store with alias bit 11 need to change coh state from B->T
Then prefetch and store miss req will be merged in the same missq
entry. Store req (2) should be able to stop prefetch (1) so that a
ping-pong process will not start