soc: bcm: bcm2835-pm: Make local symbol static

Fixes the following sparse warning:

drivers/soc/bcm/bcm2835-power.c:556:32: warning:
 symbol 'bcm2835_reset_ops' was not declared. Should it be static?

Fixes: 670c6726 ("soc: bcm: bcm2835-pm: Add support for power domains under a new binding.")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Scott Branden <scott.branden@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>