package/imx-mkimage: update hash

Due to an update in the tar logic, see commit 6e2f5d02 (download/git: fix
transform regexp for older tar versions ) - This hash needs to be updated.

Fixes:

  http://autobuild.buildroot.net/results/7c63ab1188a45d4684e159456f561a4e7c39e612/



Signed-off-by: Erik Larsson <karl.erik.larsson@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>