firewire: Kill unnecessary buf check in device_attribute.show

Per Documentation/filesystems/sysfs.rst:
> sysfs allocates a buffer of size (PAGE_SIZE) and passes it to the
> method.

So we can kill the unnecessary buf check safely.

Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
Link: https://lore.kernel.org/r/20240122053942.80648-1-lizhijian@fujitsu.com
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

Author: zhijianli88

drivers/firewire/core-device.c

@@ -322,7 +322,7 @@ static ssize_t show_immediate(struct device *dev,
 	if (value < 0)
 		return -ENOENT;
 
-	return snprintf(buf, buf ? PAGE_SIZE : 0, "0x%06x\n", value);
+	return snprintf(buf, PAGE_SIZE, "0x%06x\n", value);
 }
 
 #define IMMEDIATE_ATTR(name, key)				\
@@ -334,8 +334,6 @@ static ssize_t show_text_leaf(struct device *dev,
 	struct config_rom_attribute *attr =
 		container_of(dattr, struct config_rom_attribute, attr);
 	const u32 *directories[] = {NULL, NULL};
-	size_t bufsize;
-	char dummy_buf[2];
 	int i, ret = -ENOENT;
 
 	down_read(&fw_device_rwsem);
@@ -357,15 +355,9 @@ static ssize_t show_text_leaf(struct device *dev,
 		}
 	}
 
-	if (buf) {
-		bufsize = PAGE_SIZE - 1;
-	} else {
-		buf = dummy_buf;
-		bufsize = 1;
-	}
-
 	for (i = 0; i < ARRAY_SIZE(directories) && !!directories[i]; ++i) {
-		int result = fw_csr_string(directories[i], attr->key, buf, bufsize);
+		int result = fw_csr_string(directories[i], attr->key, buf,
+					   PAGE_SIZE - 1);
 		// Detected.
 		if (result >= 0) {
 			ret = result;