ARM: bcm: err, don't BUG() on SMC init failures

Several conditions in bcm_kona_smc_init() are handled with BUG_ON().
That function is capable of returning an error, so do that instead.

Also, don't assume of_get_address() returns a valid pointer.

Signed-off-by: Alex Elder <elder@linaro.org>
Reviewed-by: Tim Kryger <tim.kryger@linaro.org>
Reviewed-by: Markus Mayer <markus.mayer@linaro.org>
Reviewed-by: Matt Porter <mporter@linaro.org>
Signed-off-by: Matt Porter <mporter@linaro.org>