mem: fixupAddr should not panic if it fails.

mem: fixupAddr should not panic if it fails.

This function should just return false in that case, and its callers
should figure out what to do. Otherwise, when calling tryReadBlob in SE
mode, a failure to read the blob makes gem5 panic instead of just
returning false.

Change-Id: I74b9cb98f595c52300d683842ece68c6031d9b85
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/30376
Reviewed-by: Sandipan Das <sandipan@linux.ibm.com>
Reviewed-by: Matthew Poremba <matthew.poremba@amd.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>