staging: lustre: rename cfs_cpt_table to cfs_cpt_tab

The variable "cfs_cpt_table" has the same name as
the structure "struct cfs_cpt_table".
This makes it hard to use #define to make one disappear
on a uni-processor build, but keep the other.
So rename the variable to cfs_cpt_tab.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>