build: fix incorrect initramfs gzip compression

build: fix incorrect initramfs gzip compression

Requires: tools/libdeflate

fix consistency of executable to use
`$(STAGING_DIR_HOST)/bin/libdeflate-gzip`, and not system-installed ones
from the usual environment `PATH`;
this affects option `CONFIG_KERNEL_INITRAMFS_COMPRESSION_GZIP`

this may have worked in the past but only via side effect of having the
binaries on the host system (and whatever unpredictable version or
patchset those might be), and did not use the improved but totally
compatible libdeflate-gzip

Fixes: 330bd380e8b6 ("image: allow building FIT and uImage with ramdisk")
Signed-off-by: Tony Butler <spudz76@gmail.com>