ext4: remove redundant o_start statement

The if will goto out of the loop, and until the end of the
function execution, o_start will not be used again.

The clang_analyzer complains as follows:

fs/ext4/move_extent.c:635:5 warning:

Value stored to 'o_start' is never read
Reported-by: NZeal Robot <zealci@zte.com.cn>
Signed-off-by: Nluo penghao <luo.penghao@zte.com.cn>
Link: https://lore.kernel.org/r/20211208075157.404535-1-luo.penghao@zte.com.cnSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

fs/ext4/move_extent.c

@@ -632,7 +632,6 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp, __u64 orig_blk,
 		/* Check hole before the start pos */
 		if (cur_blk + cur_len - 1 < o_start) {
 			if (next_blk == EXT_MAX_BLOCKS) {
-				o_start = o_end;
 				ret = -ENODATA;
 				goto out;
 			}