serial: samsung: Removes the IRQ not found warning

In few older Samsung SoCs like s3c2410, s3c2412
and s3c2440, UART IP is having 2 interrupt lines.
However, in other SoCs like s3c6400, s5pv210,
exynos5433, and exynos4210 UART is having only 1
interrupt line. Due to this, "platform_get_irq(platdev, 1)"
call in the driver gives the following false-positive error:
"IRQ index 1 not found" on newer SoC's.

This patch adds the condition to check for Tx interrupt
only for the those SoC's which have 2 interrupt lines.

Tested-by: Alim Akhtar <alim.akhtar@samsung.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Signed-off-by: Tamseel Shams <m.shams@samsung.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200810030021.45348-1-m.shams@samsung.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/samsung_tty.c

@@ -1905,9 +1905,11 @@ static int s3c24xx_serial_init_port(struct s3c24xx_uart_port *ourport,
 		ourport->tx_irq = ret + 1;
 	}
 
+	if (!s3c24xx_serial_has_interrupt_mask(port)) {
 		ret = platform_get_irq(platdev, 1);
 		if (ret > 0)
 			ourport->tx_irq = ret;
+	}
 	/*
 	 * DMA is currently supported only on DT platforms, if DMA properties
 	 * are specified.