mfd: cros_ec_dev: Don't advertise junk features on failure

If the feature query fails during this driver's probe, we memset the
features bits to 0, but then we continue to overwrite that with whatever
junk we read back when the feature probing failed. In the case of a SPI
device, it may be complete junk, causing the caller of this function to
think certain features are present when they aren't. Don't copy over the
bad message on failure so we can fail more gracefully.

Fixes: e4244ebd

 ("platform/chrome: Introduce a new function to check EC features.")
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Acked-by: Benson Leung <bleung@chromium.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>