mfd: si476x-cmd: Add missing documentation for si476x_cmd_fm_rds_status()'s arg 'report'

Kerneldoc syntax is used, but not complete.

Descriptions are required for all arguments.

Fixes the following W=1 build warning:

 drivers/mfd/si476x-cmd.c:907: warning: Function parameter or member 'report' not described in 'si476x_core_cmd_fm_rds_status'

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

drivers/mfd/si476x-cmd.c

@@ -892,6 +892,8 @@ EXPORT_SYMBOL_GPL(si476x_core_cmd_fm_seek_start);
  *                rest RDS data contains the last valid info received
  * @mtfifo: if set the command clears RDS receive FIFO
  * @intack: if set the command clards the RDSINT bit.
+ * @report: - all signal quality information retured by the command
+ *           (if NULL then the output of the command is ignored)
  *
  * Function returns 0 on success and negative error code on failure
  */