uboot-imx

tools: image: fix message when fail to add verification data for config

This function is called when signing configuration nodes.  Adjust
the error message.

I do not know why we do not need to show the error message in case of
ENOSPC.  Remove the if-conditional that seems unnecessary.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>