tfa-layerscape: fix fiptool's build

tfa-layerscape: fix fiptool's build

A missing '\' caused the remaining parameters not to be passed to make.

This fixes the following error:

| gcc -c [...] fiptool.c -o fiptool.o
| In file included from fiptool.h:16,
|                 from fiptool.c:19:
|fiptool_platform.h:19:11: fatal error: openssl/sha.h: No such file or directory
|   19 | # include <openssl/sha.h>
|      |           ^~~~~~~~~~~~~~~
|compilation terminated.
|make[3]: *** [Makefile:58: fiptool.o] Error 1

as the HOST_CFLAGS are no longer passed.

then, HOST_CFLAGS is specified as a command argument, this
is a specific problem of our built since appending these
needs the override directive.

Fixes: df28bfe03247 ("tfa-layerscape: Change to github and use the latest tag")
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>