configs/imx23evk: Bump the U-Boot version

Thomas Petazzoni reports:

"The imx23evk_defconfig no longer builds:

  https://gitlab.com/buildroot.org/buildroot/-/jobs/158295124

This is due to the bump of OpenSSL to 1.1.x. This issue seems to have
been fixed in U-Boot commit 7bae13b7579a6bc42330427496330fe2a29cbd56,
which is part of U-Boot since 2017.01, but the defconfig is using
2016.09."

Bump to the U-Boot 2019.01 to fix this problem.

Fixes:  https://gitlab.com/buildroot.org/buildroot/-/jobs/158295124



Reported-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>