MLK-20993 i2c: rpmsg: add a BUG_ON to catch alias id issue

The alias ID must be defined in device tree, because
that will be used as BUS ID to Cortex M4. If the alias ID
not defined, linux kernel will automatically allocate one
ID which might not be the same number used in Cortex M4 and
Cortex M4 will not send msg to I2C controller.

So let's add BUG_ON to catch issue as earlier as possible to avoid
wasting efforts.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Clark Wang <xiaoning.wang@nxp.com>
(cherry picked from commit b9ff2035)