serial: doc: Re-add paragraph documenting uart_console_write()

Commit 834392a7 ("serial: doc: Un-document non-existing
uart_write_console()") removed a paragraph about a helper function that
seemed to never exist.

Peter Hurley pointed out that the function does exist, but is called
differently. Re-add the paragraph, with the function name corrected.

Fixes: 834392a7 ("serial: doc: Un-document non-existing uart_write_console()")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/serial/driver

@@ -28,6 +28,11 @@ The serial core provides a few helper functions.  This includes identifing
 the correct port structure (via uart_get_console) and decoding command line
 arguments (uart_parse_options).
 
+There is also a helper function (uart_console_write) which performs a
+character by character write, translating newlines to CRLF sequences.
+Driver writers are recommended to use this function rather than implementing
+their own version.
+
 
 Locking
 -------