ext2: code cleanup for descriptor_loc()

Code cleanup by removing unnecessary variable
in descriptor_loc().

Link: https://lore.kernel.org/r/20191115224900.2613-1-cgxu519@mykernel.net


Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
Signed-off-by: Jan Kara <jack@suse.cz>