i2c-comcerto: dev_warn about failed transfers

Print a warning if an I2C transfer fails.  We previously missed out on
such important error messages. This is particularly important because
the lm63 driver silently ignores I2C (SMBus) errors and misinterprets
return values.

Change-Id: Idce7b6e05a4088058521e41183e98a6730fca436
1 file changed