fsstress: fix incorrect if condition check for collapse range mode

fsstress: fix incorrect if condition check for collapse range mode

There is if condition to be block aligned for off and len of Collapse range.
But off and len for all fallocate opearion can be aligned by incorrect
if condition check.

Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Ashish Sangwan <a.sangwan@samsung.com>
Reviewed-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>