arch-gcn3: Fix stride bug in buffer OOB detection logic

arch-gcn3: Fix stride bug in buffer OOB detection logic

The out-of-range logic for buffer accesses is missing the top 4 bits of
const_stride when dealing with scratch buffers.  This can cause
perfectly valid scratch acceses to be suppressed when const_stride is
large.

Change-Id: I8f94d44c242fda26cf6dfb75db04fa3aca934b3e
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/29968
Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Maintainer: Anthony Gutierrez <anthony.gutierrez@amd.com>
Tested-by: kokoro <noreply+kokoro@google.com>