linux-imx

kbuild: fix compression errors getting ignored

A missing compression utility or other errors were not picked up by make
and an empty kernel image was produced.  By removing the &&, errors will
no longer be ignored.

Signed-off-by: Harald Seiler <hws@denx.de>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>