Incorrect attribute application for nested pointers

[ehaas]

This should be a single pointer to a single pointer, but the attribute gets applied twice to the outer pointer:

#include <ptrcheck.h>

void foo(int *__single *__single p) {
	p[0][5] = 5;
}

% arocc -fexperimental-bounds-safety test.c
test.c:3:25: warning: pointer annotated with single multiple times. Annotate only once to remove this warning [-Wbounds-attributes-redundant]
void foo(int *__single *__single p) {
                        ^
/Users/ehaas/source/arocc/zig-out/include/ptrcheck.h:11:33: note: expanded from here
#define __single __attribute__((__single__))
                                ^

% clang -Xclang -fexperimental-bounds-safety test.c
test.c:4:6: error: array subscript on single pointer 'p[0]' must use a constant index of 0 to be in bounds
    4 |         p[0][5] = 5;
      |         ~~~~^~
1 error generated.