staging: exfat: Fix a typo in Kconfig

This patch fix a spelling typo in Kconfig.

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Link: https://lore.kernel.org/r/20190930130504.21994-1-standby24x7@gmail.com


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