Correct some minor compiler warnings

A few places in the code through up warnings when building with strict
compiler flags. Correct these.

BUG=chrome-os-partner:21115
BRANCH=pit
TEST=manual
Build with:

FEATURES=test emerge-peach_pit vboot_reference

and see that iot now succeeds. Warnings include:

host/arch/arm/lib/crossystem_arch.c: In function 'ReadFdtValue':
host/arch/arm/lib/crossystem_arch.c:93:8: error: ignoring return value of 'fread', declared with attribute warn_unused_result [-Werror=unused-result]

Change-Id: I765723636e5f8979b794925c7b610081b2849026
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/66174
4 files changed