lightnvm: Use u64 instead of __le64 for CPU visible side

Sparse complains about using strict data types:

drivers/lightnvm/pblk-read.c:254:43: warning: incorrect type in assignment (different base types)
drivers/lightnvm/pblk-read.c:254:43:    expected restricted __le64 <noident>
drivers/lightnvm/pblk-read.c:254:43:    got unsigned long long [unsigned] [usertype] <noident>
drivers/lightnvm/pblk-read.c:255:29: warning: cast from restricted __le64
drivers/lightnvm/pblk-read.c:268:29: warning: cast from restricted __le64
drivers/lightnvm/pblk-read.c:328:41: warning: incorrect type in assignment (different base types)
drivers/lightnvm/pblk-read.c:328:41:    expected restricted __le64 <noident>
drivers/lightnvm/pblk-read.c:328:41:    got unsigned long long [unsigned] [usertype] <noident>

In the code it seems explicit that lba_list_mem and lba_list_media members
of struct pblk_pr_ctx are used on CPU side, which means they should not be
of strict types.

Change types of lba_list_mem and lba_list_media members to be u64.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Javier González <javier@javigon.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>