Kerneldoc is for documenting function arguments and return values.

Prevents warnings like:

 drivers/mfd/tc3589x.c:32: warning: Enum value 'TC3589X_TC35890' not described in enum 'tc3589x_version'
 drivers/mfd/tc3589x.c:32: warning: Enum value 'TC3589X_TC35892' not described in enum 'tc3589x_version'
 drivers/mfd/tc3589x.c:32: warning: Enum value 'TC3589X_TC35893' not described in enum 'tc3589x_version'
 drivers/mfd/tc3589x.c:32: warning: Enum value 'TC3589X_TC35894' not described in enum 'tc3589x_version'
 drivers/mfd/tc3589x.c:32: warning: Enum value 'TC3589X_TC35895' not described in enum 'tc3589x_version'
 drivers/mfd/tc3589x.c:32: warning: Enum value 'TC3589X_TC35896' not described in enum 'tc3589x_version'
 drivers/mfd/tc3589x.c:32: warning: Enum value 'TC3589X_UNKNOWN' not described in enum 'tc3589x_version'
Signed-off-by: Lee Jones <lee.jones@linaro.org>