[PATCH] I2C: inline i2c_adapter_id

We could inline i2c_adapter_id, as it is really, really short. Doing
so saves a few bytes both in i2c-core and in the drivers using this
function.

                                            before     after      diff
drivers/hwmon/adm1026.ko                     41344     41305       -39
drivers/hwmon/asb100.ko                      27325     27246       -79
drivers/hwmon/gl518sm.ko                     20824     20785       -39
drivers/hwmon/it87.ko                        26419     26380       -39
drivers/hwmon/lm78.ko                        21424     21385       -39
drivers/hwmon/lm85.ko                        41034     40939       -95
drivers/hwmon/w83781d.ko                     39561     39514       -47
drivers/hwmon/w83792d.ko                     32979     32932       -47
drivers/i2c/i2c-core.ko                      24708     24531      -177

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>