staging: exfat: cleanup spacing for casts

Fix checkpatch.pl warnings:

  CHECK: No space is necessary after a cast

Signed-off-by: Valentin Vidic <vvidic@valentin-vidic.from.hr>
Link: https://lore.kernel.org/r/20190908152616.25459-2-vvidic@valentin-vidic.from.hr


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>