ext2: remove redundant assignment to variable desc and variable best_desc

Variable desc is being assigned a value that is never read, the exit
via label found immeditely returns with no access to desc. The
assignment is redundant and can be removed. Also remove variable best_desc
since this is not used. Cleans up clang scan muild warning:

fs/ext2/ialloc.c:297:4: warning: Value stored to 'desc' is never
read [deadcode.DeadStores]

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <20230630165458.166238-1-colin.i.king@gmail.com>