vt: fix kernel-doc warnings in ucs_get_fallback()

Use the correct function parameter name in ucs_get_fallback() to prevent
kernel-doc warnings:

Warning: drivers/tty/vt/ucs.c:218 function parameter 'cp' not described in 'ucs_get_fallback'
Warning: drivers/tty/vt/ucs.c:218 Excess function parameter 'base' description in 'ucs_get_fallback'

Fixes: fe26933 ("vt: add ucs_get_fallback()")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Nicolas Pitre <npitre@baylibre.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: linux-serial@vger.kernel.org
Reviewed-by: Nicolas Pitre <npitre@baylibre.com>.
Link: https://lore.kernel.org/r/20250611020229.2650595-1-rdunlap@infradead.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: rddunlap

drivers/tty/vt/ucs.c

@@ -206,7 +206,7 @@ static int ucs_page_entry_cmp(const void *key, const void *element)
 
 /**
  * ucs_get_fallback() - Get a substitution for the provided Unicode character
- * @base: Base Unicode code point (UCS-4)
+ * @cp: Unicode code point (UCS-4)
  *
  * Get a simpler fallback character for the provided Unicode character.
  * This is used for terminal display when corresponding glyph is unavailable.