staging: exfat: use prandom_u32() for i_generation

Similar to commit 46c9a946 ("shmem: use monotonic time for i_generation")
we should not use the deprecated get_seconds() interface for i_generation.

prandom_u32() is the replacement used in other file systems.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Link: https://lore.kernel.org/r/20191108213257.3097633-2-arnd@arndb.de


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