[Darwin] Invert the logic for getting the path to use for the KVS as …

…it was inverted by mistake in #15586 (#15676)

src/platform/Darwin/KeyValueStoreManagerImpl.mm

@@ -156,7 +156,7 @@ - (instancetype)initWithContext:(nonnull NSManagedObjectContext *)context key:(n
             ReturnErrorCodeIf(filepath == nil, CHIP_ERROR_INVALID_ARGUMENT);
 
             // relative paths are relative to Documents folder
-            if ([filepath hasPrefix:@"/"]) {
+            if (![filepath hasPrefix:@"/"]) {
                 NSURL * documentsDirectory = [NSFileManager.defaultManager URLForDirectory:NSDocumentDirectory
                                                                                   inDomain:NSUserDomainMask
                                                                          appropriateForURL:nil