mm/swap_slots.c: remove redundant check for swap_slot_cache_initialized

Because enable_swap_slots_cache can only become true in
enable_swap_slots_cache(), and depends on swap_slot_cache_initialized is
true before.  That means, when enable_swap_slots_cache is true,
swap_slot_cache_initialized is true also.

So the condition:
"swap_slot_cache_enabled && swap_slot_cache_initialized"
can be reduced to "swap_slot_cache_enabled"

And in mathematics:
"!swap_slot_cache_enabled || !swap_slot_cache_initialized"
is equal to "!(swap_slot_cache_enabled && swap_slot_cache_initialized)"

So no functional change.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Tim Chen <tim.c.chen@linux.intel.com>
Link: http://lkml.kernel.org/r/20200430061143.450-4-thunder.leizhen@huawei.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/swap_slots.c

@@ -46,8 +46,7 @@ static void __drain_swap_slots_cache(unsigned int type);
 static void deactivate_swap_slots_cache(void);
 static void reactivate_swap_slots_cache(void);
 
-#define use_swap_slot_cache (swap_slot_cache_active && \
-		swap_slot_cache_enabled && swap_slot_cache_initialized)
+#define use_swap_slot_cache (swap_slot_cache_active && swap_slot_cache_enabled)
 #define SLOTS_CACHE 0x1
 #define SLOTS_CACHE_RET 0x2
 
@@ -94,7 +93,7 @@ static bool check_cache_active(void)
 {
 	long pages;
 
-	if (!swap_slot_cache_enabled || !swap_slot_cache_initialized)
+	if (!swap_slot_cache_enabled)
 		return false;
 
 	pages = get_nr_swap_pages();