The alignment is passed into contigmalloc_domainset in the 7th argument.

KUBSAN was complaining the pointer contigmalloc_domainset returned was
misaligned. Fix this by using the correct argument to find the alignment
in the function signature.

Reported by:	KUBSAN
MFC after:	2 weeks
Sponsored by:	DARPA, AFRL

sys/sys/malloc.h

@@ -177,7 +177,7 @@ void	*contigmalloc(unsigned long size, struct malloc_type *type, int flags,
 void	*contigmalloc_domainset(unsigned long size, struct malloc_type *type,
 	    struct domainset *ds, int flags, vm_paddr_t low, vm_paddr_t high,
 	    unsigned long alignment, vm_paddr_t boundary)
-	    __malloc_like __result_use_check __alloc_size(1) __alloc_align(6);
+	    __malloc_like __result_use_check __alloc_size(1) __alloc_align(7);
 void	free(void *addr, struct malloc_type *type);
 void	free_domain(void *addr, struct malloc_type *type);
 void	*malloc(size_t size, struct malloc_type *type, int flags) __malloc_like