tty: serial: cpm_uart: remove unused cpm_uart_nr declaration

cpm_uart_nr has been removed since
commit 0b2a2e5b77 ("cpm_uart: Remove !CONFIG_PPC_CPM_NEW_BINDING
code"), so remove it.

Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Link: https://lore.kernel.org/r/20220911093654.3222701-1-cuigaosheng1@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/cpm_uart/cpm_uart.h

@@ -87,7 +87,6 @@ struct uart_cpm_port {
 	struct gpio_desc	*gpios[NUM_GPIOS];
 };
 
-extern int cpm_uart_nr;
 extern struct uart_cpm_port cpm_uart_ports[UART_NR];
 
 /* these are located in their respective files */