OMAP2+: hwmod: Remove _populate_mpu_rt_base warning

It is perfectly valid for some hwmod to not have any
register target address for sysconfig. This is especially
true for interconnect hwmods.
Remove the warning.

Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>