ext2: initialize quota info in ext2_xattr_set()

In order to correctly account/limit space usage, should initialize
quota info before calling quota related functions.

Link: https://lore.kernel.org/r/20200626054959.114177-1-cgxu519@mykernel.net


Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
Reviewed-by: Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
Signed-off-by: Jan Kara <jack@suse.cz>