disk: Rename grub_disk_get_size() to grub_disk_native_sectors()

The function grub_disk_get_size() is confusingly named because it actually
returns a sector count where the sectors are sized in the GRUB native sector
size. Rename to something more appropriate.

Suggested-by: Daniel Kiper <daniel.kiper@oracle.com>
Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Patrick Steinhardt <ps@pks.im>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/kern/disk.c

@@ -533,7 +533,7 @@ grub_disk_read (grub_disk_t disk, grub_disk_addr_t sector,
 }
 
 grub_uint64_t
-grub_disk_get_size (grub_disk_t disk)
+grub_disk_native_sectors (grub_disk_t disk)
 {
   if (disk->partition)
     return grub_partition_get_len (disk->partition);