devlink: correct misspelling of snapshot

The function to obtain a unique snapshot id was mistakenly typo'd as
devlink_region_shapshot_id_get. Fix this typo by renaming the function
and all of its users.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>