SBI calls expect a pointer to a u_long rather than a pointer.
This is just cosmetic.
A weirder issue is that the SBI doc claims the hart mask pointer should
be a physical address, not a virtual address. However, the implementation
in bbl seems to just dereference the address directly.
Reviewed by: markj
Sponsored by: DARPA
Differential Revision: https://reviews.freebsd.org/D17781