base: Fix copyright of base/stats/SConscript

base: Fix copyright of base/stats/SConscript

The original copyright was accidentally removed by
e59557af500d1633b1f41b023d6c072acaf145a0.

Change-Id: Ib3b7a34ea889fbd9a6f2a8e21a6bb24432939da9
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40755
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>