pinctrl: Fix grammar in pinmux request list

- The combination of a FUNCTION and a PIN GROUP determine a certain function

  for a certain set of pins. The knowledge of the functions and pin groups

  and their machine-specific particulars are kept inside the pinmux driver,

  from the outside only the enumerators are known, and the driver core can:

  from the outside only the enumerators are known, and the driver core can

  request:

  - Request the name of a function with a certain selector (>= 0)

  - The name of a function with a certain selector (>= 0)

  - A list of groups associated with a certain function

  - Request that a certain group in that list to be activated for a certain

    function

  - That a certain group in that list to be activated for a certain function

  As already described above, pin groups are in turn self-descriptive, so

  the core will retrieve the actual pin range in a certain group from the