jbd2: remove redundant assignement to variable err

The variable err is being assigned a value that is never read, it
is being re-assigned inside the following while loop and also
after the while loop. The assignment is redundant and can be
removed.

Cleans up clang scan build warning:
fs/jbd2/commit.c:574:2: warning: Value stored to 'err' is never
read [deadcode.DeadStores]

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20240410112803.232993-1-colin.i.king@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>