sim-se: minor refactor for ProcessParams::create

Remove the nullptr initialization and change the message
for object file failure.

Change-Id: I14b80b47b65893c55810e7f715c1b8fc643c5125
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/19949
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed