devlink: Use DIV_ROUND_UP_ULL in DEVLINK_HEALTH_SIZE_TO_BUFFERS

When building this code on a 32-bit platform such as ARM, there is a
link time error (lld error shown, happpens with ld.bfd too):

ld.lld: error: undefined symbol: __aeabi_uldivmod
>>> referenced by devlink.c
>>>               net/core/devlink.o:(devlink_health_buffers_create) in archive built-in.a

This happens when using a regular division symbol with a u64 dividend.
Use DIV_ROUND_UP_ULL, which wraps do_div, to avoid this situation.

Fixes: cb5ccfbe ("devlink: Add health buffer support")
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>