busybox

i2cdump: bail-out if block read fails

We should bail-out if i2c_smbus_read_block_data() or
i2c_smbus_read_i2c_block_data() return 0 or less. Add the missing check
for the former and fix the existing for the latter.

Signed-off-by: Bartosz Golaszewski <bartekgola@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>