pinctrl: assume map table entries can't have a NULL name field
pinctrl_register_mappings() already requires that every mapping table
entry have a non-NULL name field.
Logically, this makes sense too; drivers should always request a specific
named state so they know what they're getting. Relying on getting the
first mentioned state in the mapping table is error-prone, and a nasty
special case to implement, given that a given the mapping table may define
multiple states for a device.
Remove a small part of the documentation that talked about optionally
requesting a specific state; it's mandatory now.