ext4: remove redundant checking in ext4_ioctl_checkpoint

It is already checked after comment "check for invalid bits set",
so let's remove this one.

Signed-off-by: Guoqing Jiang <guoqing.jiang@linux.dev>
Link: https://lore.kernel.org/r/20220918115219.12407-1-guoqing.jiang@linux.dev


Signed-off-by: Theodore Ts'o <tytso@mit.edu>