Avoid multiple compiler warnings such as the following:
main.c: In function ‘update’:
main.c:157:4: warning: pointer targets in passing argument 1 of ‘mem_getusage’ differ in signedness [-Wpointer-sign]
mem_getusage(&mem_usage, &swap_usage, &mem_opts);
^
In file included from main.c:29:0:
mem.h:16:6: note: expected ‘int *’ but argument is of type ‘unsigned int *’
void mem_getusage(int *per_mem, int *per_swap, const struct mem_options *opts);
^
