libcbfs: Fix legacy CBFS API, typos

Pulling CBFS fix from libpayload: http://review.coreboot.org/#/c/2455/2

get_cbfs_header expects CBFS_HEADER_INVALID_ADDRESS (0xffffffff)
instead of NULL when something is wrong.
Also, fix typo.

Change-Id: I7f393f7c24f74a3358f7339a3095b0d845bdc02d
Signed-off-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-on: http://review.coreboot.org/2457
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
1 file changed