samples: subsys: nvs: Print rc on errors

So that the user gets a hint of what the problem can be.

Signed-off-by: Lluis Campos <lluis.campos@northern.tech>

samples/subsys/nvs/src/main.c

@@ -86,15 +86,15 @@ int main(void)
 	fs.offset = NVS_PARTITION_OFFSET;
 	rc = flash_get_page_info_by_offs(fs.flash_device, fs.offset, &info);
 	if (rc) {
-		printk("Unable to get page info\n");
+		printk("Unable to get page info, rc=%d\n", rc);
 		return 0;
 	}
 	fs.sector_size = info.size;
 	fs.sector_count = 3U;
 
 	rc = nvs_mount(&fs);
 	if (rc) {
-		printk("Flash Init failed\n");
+		printk("Flash Init failed, rc=%d\n", rc);
 		return 0;
 	}