ec/chromeec: fix LPC read/write for MEC devices

Commit 8cf8aa2 [ec/google/chromeec: Use common MEC interface]
changed the return mechanism for the checksum on reads/writes
for MEC devices, but incorrectly handled the passed-in csum
parameter by not dereferencing. This led to the returned csum
value always being zero, which causes all EC commands with non-
NULL data_in to fail with a checksum error.

Fix this by storing the returned checksum in a temp variable,
and only assigning to csum when the pointer isn't NULL;

Test: build/boot google/chell, verify EC hello command succeeds,
keyboard backlight turned on at boot.

Change-Id: I7122c3fdc5a19f87f12975ee448728cf29948436
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/c/30444
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

0 files changed, 0 insertions, 0 deletions