block/rnbd-clt-sysfs: Remove copy buffer overlap in rnbd_clt_get_path_name

cppcheck report the following error:
  rnbd/rnbd-clt-sysfs.c:522:36: error: The variable 'buf' is used both
  as a parameter and as destination in snprintf(). The origin and
  destination buffers overlap. Quote from glibc (C-library)
  documentation
  (http://www.gnu.org/software/libc/manual/html_mono/libc.html#Formatted-Output-Functions):
  "If copying takes place between objects that overlap as a result of a
  call to sprintf() or snprintf(), the results are undefined."
  [sprintfOverlappingData]
Fix it by initializing the buf variable in the first snprintf call.

Fixes: 91f4acb2 ("block/rnbd-clt: support mapping two devices")
Signed-off-by: NDima Stepanov <dmitrii.stepanov@ionos.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: NJack Wang <jinpu.wang@ionos.com>
Signed-off-by: NGioh Kim <gi-oh.kim@cloud.ionos.com>
Reviewed-by: NChaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Link: https://lore.kernel.org/r/20210419073722.15351-19-gi-oh.kim@ionos.comSigned-off-by: NJens Axboe <axboe@kernel.dk>

drivers/block/rnbd/rnbd-clt-sysfs.c

@@ -514,11 +514,7 @@ static int rnbd_clt_get_path_name(struct rnbd_clt_dev *dev, char *buf,
 	while ((s = strchr(pathname, '/')))
 		s[0] = '!';
 
-	ret = snprintf(buf, len, "%s", pathname);
-	if (ret >= len)
-		return -ENAMETOOLONG;
-
-	ret = snprintf(buf, len, "%s@%s", buf, dev->sess->sessname);
+	ret = snprintf(buf, len, "%s@%s", pathname, dev->sess->sessname);
 	if (ret >= len)
 		return -ENAMETOOLONG;