perf/arm-cmn: Fix REQ2/SNP2 mixup

Somehow the encodings for REQ2/SNP2 channels in XP events
got mixed up... Unmix them.

CC: stable@vger.kernel.org
Fixes: 23760a01 ("perf/arm-cmn: Add CMN-700 support")
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/087023e9737ac93d7ec7a841da904758c254cb01.1746717400.git.robin.murphy@arm.com


Signed-off-by: Will Deacon <will@kernel.org>