Compare the number of bytes actually seen on the wire to the byte
count field returned by the slave device.

Previously we just overwrote the byte count returned by the slave
with the real byte count and let the caller figure out if the
message was sane.
Signed-off-by: NStephen Douthit <stephend@adiengineering.com>
Tested-by: NDan Priamo <danp@adiengineering.com>
Acked-by: NNeil Horman <nhorman@tuxdriver.com>
Signed-off-by: NWolfram Sang <wsa@the-dreams.de>
Cc: stable@kernel.org