ext4: fix unsigned long long printk warning in super.c

sparc64 allmodconfig:

fs/ext4/super.c: In function `lifetime_write_kbytes_show':
fs/ext4/super.c:2174: warning: long long unsigned int format, long unsigned int arg (arg 4)
fs/ext4/super.c:2174: warning: long long unsigned int format, long unsigned int arg (arg 4)

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>