ext4: remove redundant assignment to variable split_flag1

ext4: remove redundant assignment to variable split_flag1

Variable split_flag1 is being assigned a value that is never read,
it is being re-assigned a new value in the following code block.
The assignment is redundant and can be removed.

Cleans up clang scan build warning:
fs/ext4/extents.c:3371:2: warning: Value stored to 'split_flag1' is
never read [deadcode.DeadStores]

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://lore.kernel.org/r/20220301121644.997833-1-colin.i.king@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>