fix base image build error due to unable to locate sshd-regen-keys

Base image build failed with error:
> | DEBUG: Executing shell function rootfs_install_pkgs_download
> | Reading package lists...
> | Building dependency tree...
> | Reading state information...
> | E: Unable to locate package sshd-regen-keys
> | WARNING: exit code 100 from a shell command.
> | DEBUG: Executing shell function rootfs_do_umounts
> | DEBUG: Shell function rootfs_do_umounts finished
> | DEBUG: Python function do_rootfs_install finished

use IMAGE_INSTALL instead of IMAGE_PREINSTALL to fix the issue as sshd-regen-keys is
provided by isar.

Signed-off-by: Anantha K R <anantha.kr@siemens.com>

Author: Anantha K R

meta/recipes-core/images/iot2050-image-base.bb

@@ -13,7 +13,7 @@ inherit image
 
 DESCRIPTION = "IOT2050 Debian Base Image"
 
-IMAGE_PREINSTALL += "sshd-regen-keys"
+IMAGE_INSTALL += "sshd-regen-keys"
 
 IMAGE_INSTALL += "${IOT2050_META_PACKAGES}"