programmer.h: Convert anon union to anon struct

Convert the anon union of registered masters in the mst
field of the flashctx to a anon struct. If we are going
to dereference a pointer there in an undefined way we
should crash and not plow ahead with invalid memory.

i.e., As a minimal example,
```

struct idk {
	struct {
		int *a;
		int *b;
	};
};

int main()
{
	struct idk foo = {0};
	int i = 12;
	foo.a = &i;
	printf("%d\n", *foo.b);
	return 0;
}
```

The user of the registered_masters type is therefore
responsible for querying the buses_supported field before
attempting to dereference a ptr field in the anon struct.

BUG=?
TEST=<needed>

Change-Id: I576967a8599b923c902e39f177f39146291cc242
Signed-off-by: Edward O'Callaghan <quasisec@google.com>
---
M programmer.h
1 file changed, 1 insertion(+), 1 deletion(-)