kprobes: Add missing kerneldoc for __get_insn_slot

Add kerneldoc for '__get_insn_slot' function to fix W=1 warnings:

  kernel/kprobes.c:141 function parameter 'c' not described in '__get_insn_slot'

Link: https://lore.kernel.org/all/20250704143817707TOCcfTRWsO5OAbQ2eYoU9@zte.com.cn/

Signed-off-by: Peng Jiang <jiang.peng9@zte.com.cn>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Author: Jump2233

kernel/kprobes.c

@@ -135,8 +135,12 @@ struct kprobe_insn_cache kprobe_insn_slots = {
 static int collect_garbage_slots(struct kprobe_insn_cache *c);
 
 /**
- * __get_insn_slot() - Find a slot on an executable page for an instruction.
- * We allocate an executable page if there's no room on existing ones.
+ * __get_insn_slot - Find a slot on an executable page for an instruction.
+ * @c: Pointer to kprobe instruction cache
+ *
+ * Description: Locates available slot on existing executable pages,
+ *              allocates an executable page if there's no room on existing ones.
+ * Return: Pointer to instruction slot on success, NULL on failure.
  */
 kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c)
 {