super.c: unused variable warning without CONFIG_QUOTA

sb info is only checked with quota support.

fs/ext4/super.c: In function ‘parse_options’:
fs/ext4/super.c:1600:23: warning: unused variable ‘sbi’ [-Wunused-variable]

Signed-off-by: Eldad Zack <eldad@fogrefinery.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>