serial: sh-sci: Don't allow CS5-6

stable inclusion
from stable-v5.10.122
commit a9f6bee486e7b33579dceddc99bcb30152c77454
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5W6OE

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a9f6bee486e7b33579dceddc99bcb30152c77454

--------------------------------

[ Upstream commit 9b87162d ]

Only CS7 and CS8 seem supported but CSIZE is not sanitized from
CS5 or CS6 to CS8.

Set CSIZE correctly so that userspace knows the effective value.
Incorrect CSIZE also results in miscalculation of the frame bits in
tty_get_char_size() or in its predecessor where the roughly the same
code is directly within uart_update_timeout().

Fixes: 1da177e4 (Linux-2.6.12-rc2)
Signed-off-by: NIlpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220519081808.3776-6-ilpo.jarvinen@linux.intel.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>

drivers/tty/serial/sh-sci.c

@@ -2392,8 +2392,12 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios,
 	int best_clk = -1;
 	unsigned long flags;
 
-	if ((termios->c_cflag & CSIZE) == CS7)
+	if ((termios->c_cflag & CSIZE) == CS7) {
 		smr_val |= SCSMR_CHR;
+	} else {
+		termios->c_cflag &= ~CSIZE;
+		termios->c_cflag |= CS8;
+	}
 	if (termios->c_cflag & PARENB)
 		smr_val |= SCSMR_PE;
 	if (termios->c_cflag & PARODD)