mem-ruby: fix functional reads in abstract ctrl

mem-ruby: fix functional reads in abstract ctrl

When calling functionalMemoryRead we need to check the mem req. queue
first as it may have write data not yet forwarded to the memory port.

Change-Id: Id37aa0837a3462d92ae9ac3b45ca756b2c4f7d97
Signed-off-by: Tiago Mück <tiago.muck@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/41153
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>