mfd: si476x-i2c: Add description for si476x_core_fwver_to_revision()'s arg 'func'

Kerneldoc syntax is used, but not complete.

Descriptions are required for all arguments.

Fixes the following W=1 build warning:

 drivers/mfd/si476x-i2c.c:550: warning: Function parameter or member 'func' not described in 'si476x_core_fwver_to_revision'

Cc: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/si476x-i2c.c

@@ -534,6 +534,11 @@ static irqreturn_t si476x_core_interrupt(int irq, void *dev)
 /**
  * si476x_firmware_version_to_revision()
  * @core: Core device structure
+ * @func: Selects the boot function of the device:
+ *         *_BOOTLOADER  - Boot loader
+ *         *_FM_RECEIVER - FM receiver
+ *         *_AM_RECEIVER - AM receiver
+ *         *_WB_RECEIVER - Weatherband receiver
  * @major:  Firmware major number
  * @minor1: Firmware first minor number
  * @minor2: Firmware second minor number