libperf xyarray: Add bounds checks to xyarray__entry()

xyarray__entry() is missing any bounds checking yet often the x and y
parameters come from external callers. Add bounds checks and an
unchecked __xyarray__entry().

Committer notes:

Make the 'x' and 'y' arguments to the new xyarray__entry() that does
bounds check to be of type 'size_t', so that we cover also the case
where 'x' and 'y' could be negative, which is needed anyway as having
them as 'int' breaks the build with:

/home/acme/git/perf/tools/lib/perf/include/internal/xyarray.h: In function ‘xyarray__entry’:
/home/acme/git/perf/tools/lib/perf/include/internal/xyarray.h:28:8: error: comparison of integer expressions of different signedness: ‘int’ and ‘size_t’ {aka ‘long unsigned int’} [-Werror=sign-compare]
28 | if (x >= xy->max_x || y >= xy->max_y)
| ^~
/home/acme/git/perf/tools/lib/perf/include/internal/xyarray.h:28:26: error: comparison of integer expressions of different signedness: ‘int’ and ‘size_t’ {aka ‘long unsigned int’} [-Werror=sign-compare]
28 | if (x >= xy->max_x || y >= xy->max_y)
| ^~
cc1: all warnings being treated as errors

Signed-off-by: Rob Herring <[e-mail]>
Suggested-by: Arnaldo Carvalho de Melo <[e-mail]>
Suggested-by: Namhyung Kim <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/lib/perf/include/internal/xyarray.h

···
 void xyarray__delete(struct xyarray *xy);
 void xyarray__reset(struct xyarray *xy);
 
-static inline void *xyarray__entry(struct xyarray *xy, int x, int y)
+static inline void *__xyarray__entry(struct xyarray *xy, int x, int y)
 {
 	return &xy->contents[x * xy->row_size + y * xy->entry_size];
+}
+
+static inline void *xyarray__entry(struct xyarray *xy, size_t x, size_t y)
+{
+	if (x >= xy->max_x || y >= xy->max_y)
+		return NULL;
+	return __xyarray__entry(xy, x, y);
 }
 
 static inline int xyarray__max_y(struct xyarray *xy)