tty: serial: sifive: Struct headers should start with 'struct <name>'

Also supply a missing member description.

Fixes the following W=1 kernel build warning(s):

 drivers/tty/serial/sifive.c:157: warning: cannot understand function prototype: 'struct sifive_serial_port '

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: linux-serial@vger.kernel.org
Cc: linux-riscv@lists.infradead.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>
Acked-by: Palmer Dabbelt <palmerdabbelt@google.com>
Link: https://lore.kernel.org/r/20201104193549.4026187-26-lee.jones@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sifive.c

@@ -144,12 +144,13 @@
  */
 
 /**
- * sifive_serial_port - driver-specific data extension to struct uart_port
+ * struct sifive_serial_port - driver-specific data extension to struct uart_port
  * @port: struct uart_port embedded in this struct
  * @dev: struct device *
  * @ier: shadowed copy of the interrupt enable register
  * @clkin_rate: input clock to the UART IP block.
  * @baud_rate: UART serial line rate (e.g., 115200 baud)
+ * @clk: reference to this device's clock
  * @clk_notifier: clock rate change notifier for upstream clock changes
  *
  * Configuration data specific to this SiFive UART.