staging: lustre: lov: use u64 instead of loff_t in lov_object_fiemap()

Change loff_t to u64 in lov_object_fiemap() since loff_t is a signed
value type.

Otherwise there could be an overflow in
drivers/staging/lustre/lustre/lov/lov_object.c:1241 lov_object_fiemap()
warn: signed overflow undefined. 'fm_start + fm_length < fm_start'

Signed-off-by: Bobi Jam <bobijam.xu@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-8773
Reviewed-on: https://review.whamcloud.com/23461


Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>