i2c: brcmstb: Use dev_name() for adapter name

This make it easier to disambiguate the different i2c controllers
present in a system, and then correlating with /proc/interrupts allows
to know which instance is interrupt driven and which one is not.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>