uboot-tools: fix dynamic linking against OpenSSL

Commit 95f9a5c3 fixed the static
linking issue of uboot-tools mkimage against OpenSSL, but in the
process broke the dynamic linking case. This commit adjusts the
uboot-tools patch to make sure both static and dynamic linking work.

An updated version of the patch has been submitted upstream.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>