serial: samsung: Fix build error

Fixes the following build error due to a typo introduced
by commit e4ac92df27 ("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 <[e-mail]>
Signed-off-by: Sachin Kamat <[e-mail]>
Signed-off-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Christian Engelmayer <[e-mail]>
Acked-by: Joe Perches <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/samsung.c

···
 	char buff[256];
 
 	va_start(va, fmt);
-	vscnprintf(buff, sizeof(buf), fmt, va);
+	vscnprintf(buff, sizeof(buff), fmt, va);
 	va_end(va);
 
 	printascii(buff);