serial: samsung: Fix build error

Fixes the following build error due to a typo introduced
by commit e4ac92d ("serial: samsung: Neaten dbg uses"):
drivers/tty/serial/samsung.c:69:26: error: ‘buf’ undeclared (first use in this function)

Reported-by: Arun Kumar K <arun.kk@samsung.com>
Signed-off-by: Sachin Kamat <sachin.kamat@samsung.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Christian Engelmayer <cengelma@gmx.at>
Acked-by: Joe Perches <joe@perches.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/samsung.c

@@ -66,7 +66,7 @@ static void dbg(const char *fmt, ...)
 	char buff[256];
 
 	va_start(va, fmt);
-	vscnprintf(buff, sizeof(buf), fmt, va);
+	vscnprintf(buff, sizeof(buff), fmt, va);
 	va_end(va);
 
 	printascii(buff);