intel/tools/aub: print better error message when mmap fails

intel/tools/aub: print better error message when mmap fails

Aubinator creates lots of 4k mappings, so for large traces it's
possible to hit system limit on the number of mappings created
by a single process.

Ideally, aubinator should merge those mappings, but that's tricky
and I'm not sure it's worth spending time on.

Signed-off-by: Marcin Ślusarz <marcin.slusarz@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8988>