drm/xe: Prefer struct_size over open coded arithmetic

This is an effort to get rid of all multiplications from allocation
functions in order to prevent integer overflows [1].

As the "q" variable is a pointer to "struct xe_exec_queue" and this
structure ends in a flexible array:

struct xe_exec_queue {
	[...]
	struct xe_lrc lrc[];
};

the preferred way in the kernel is to use the struct_size() helper to
do the arithmetic instead of the argument "size + size * count" in the
kzalloc() function.

This way, the code is more readable and more safer.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments [1]
Link: KSPP#160 [2]
Signed-off-by: Erick Archer <erick.archer@gmx.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240210141913.6611-1-erick.archer@gmx.com

Author: Erick Archer

drivers/gpu/drm/xe/xe_exec_queue.c

@@ -46,7 +46,7 @@ static struct xe_exec_queue *__xe_exec_queue_alloc(struct xe_device *xe,
 	/* only kernel queues can be permanent */
 	XE_WARN_ON((flags & EXEC_QUEUE_FLAG_PERMANENT) && !(flags & EXEC_QUEUE_FLAG_KERNEL));
 
-	q = kzalloc(sizeof(*q) + sizeof(struct xe_lrc) * width, GFP_KERNEL);
+	q = kzalloc(struct_size(q, lrc, width), GFP_KERNEL);
 	if (!q)
 		return ERR_PTR(-ENOMEM);