mfd: cros-ec: Fix host command buffer size

For SPI, we can get up to 32 additional bytes for response preamble.
The current overhead (2 bytes) may cause problems when we try to receive
a big response. Update it to 32 bytes.

Without this fix we could see a kernel BUG when we receive a big response
from the Chrome EC when is connected via SPI.
Signed-off-by: NVic Yang <victoryang@google.com>
Tested-by: Enric Balletbo i Serra <enric.balletbo.collabora.com>
Signed-off-by: NLee Jones <lee.jones@linaro.org>

include/linux/mfd/cros_ec.h

@@ -35,10 +35,11 @@
  * Max bus-specific overhead incurred by request/responses.
  * I2C requires 1 additional byte for requests.
  * I2C requires 2 additional bytes for responses.
+ * SPI requires up to 32 additional bytes for responses.
  * */
 #define EC_PROTO_VERSION_UNKNOWN	0
 #define EC_MAX_REQUEST_OVERHEAD		1
-#define EC_MAX_RESPONSE_OVERHEAD	2
+#define EC_MAX_RESPONSE_OVERHEAD	32
 
 /*
  * Command interface between EC and AP, for LPC, I2C and SPI interfaces.