tty/isicom: Fix a possible sleep-in-atomic bug in WaitTillCardIsFree

The driver may sleep under a spinlock.
The function call paths are:
isicom_activate (acquire the spinlock)
  isicom_setup_board
    drop_dtr_rts
      WaitTillCardIsFree
        msleep --> may sleep

isicom_set_termios
  isicom_config_port
    drop_dtr
      WaitTillCardIsFree
        msleep --> may sleep

isicom_tiocmset
  drop_dtr
    WaitTillCardIsFree
      msleep --> may sleep

Though "in_atomic" is used to check atomic context,
but it is not recommended to use in driver code (see include/linux/preempt.h).

To fix it, only using mdelay instead.

This bug is found by my static analysis tool(DSAC) and checked by my code review.
Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/isicom.c

@@ -219,13 +219,9 @@ static struct isi_port  isi_ports[PORT_COUNT];
 static int WaitTillCardIsFree(unsigned long base)
 {
 	unsigned int count = 0;
-	unsigned int a = in_atomic(); /* do we run under spinlock? */
 
 	while (!(inw(base + 0xe) & 0x1) && count++ < 100)
-		if (a)
-			mdelay(1);
-		else
-			msleep(1);
+		mdelay(1);
 
 	return !(inw(base + 0xe) & 0x1);
 }