soc: bcm: bcm2835-pm: Fix error paths of initialization.

The clock driver may probe after ours and so we need to pass the
-EPROBE_DEFER out.  Fix the other error path while we're here.

v2: Use dom->name instead of dom->gov as the flag for initialized
    domains, since we aren't setting up a governor.  Make sure to
    clear ->clk when no clk is present in the DT.

Signed-off-by: Eric Anholt <eric@anholt.net>
Fixes: 670c6726 ("soc: bcm: bcm2835-pm: Add support for power domains under a new binding.")