mem: Use getGuestByteOrder in the indirect memory prefetcher.
mem: Use getGuestByteOrder in the indirect memory prefetcher.

Use that instead of accessing TheISA::GuestByteOrder directly.

Change-Id: I6fbeb7501aceadb95739bb482215097af18da2fa
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/32926
Reviewed-by: Daniel Carvalho <91779fc734d358d9575ec4910de29bfcbcaf1b22@yahoo.com.br>
Maintainer: Gabe Black <5c8aa1266c03186393d9e7b3b4e3b14239af8201@google.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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