UBIFS: fix complaints about too small debug buffer size

When debugging is enabled, we use a temporary on-stack buffer for formatting
the key strings like "(11368871, direntry, 0xcd0750)". The buffer size is
32 bytes and sometimes it is not enough to fit the key string - e.g., when
inode numbers are high. This is not fatal, but the key strings are incomplete
and UBIFS complains like this:

	UBIFS assert failed in dbg_snprintf_key at 137 (pid 1)

This is a regression caused by "515315a1 UBIFS: fix key printing".

Fix the issue by increasing the buffer to 48 bytes.
Reported-by: Michael Hench <michaelhench@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Tested-by: Michael Hench <michaelhench@gmail.com>
Cc: stable@vger.kernel.org [v3.3+]

fs/ubifs/debug.h

@@ -167,7 +167,7 @@ struct ubifs_global_debug_info {
 #define ubifs_dbg_msg(type, fmt, ...) \
 	pr_debug("UBIFS DBG " type ": " fmt "\n", ##__VA_ARGS__)
 
-#define DBG_KEY_BUF_LEN 32
+#define DBG_KEY_BUF_LEN 48
 #define ubifs_dbg_msg_key(type, key, fmt, ...) do {                            \
 	char __tmp_key_buf[DBG_KEY_BUF_LEN];                                   \
 	pr_debug("UBIFS DBG " type ": " fmt "%s\n", ##__VA_ARGS__,             \