tty: actually undefine superseded ASYNC flags

Some kernel-internal ASYNC flags have been superseded by tty-port flags
and should no longer be used by kernel drivers.

Fix the misspelled "__KERNEL__" compile guards which failed their sole
purpose to break out-of-tree drivers that have not yet been updated.

Fixes: 5c0517fe ("tty: core: Undefine ASYNC_* flags superceded by TTY_PORT* flags")
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210407095208.31838-2-johan@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/uapi/linux/tty_flags.h

@@ -39,7 +39,7 @@
  * WARNING: These flags are no longer used and have been superceded by the
  *	    TTY_PORT_ flags in the iflags field (and not userspace-visible)
  */
-#ifndef _KERNEL_
+#ifndef __KERNEL__
 #define ASYNCB_INITIALIZED	31 /* Serial port was initialized */
 #define ASYNCB_SUSPENDED	30 /* Serial port is suspended */
 #define ASYNCB_NORMAL_ACTIVE	29 /* Normal device is active */
@@ -81,7 +81,7 @@
 #define ASYNC_SPD_WARP		(ASYNC_SPD_HI|ASYNC_SPD_SHI)
 #define ASYNC_SPD_MASK		(ASYNC_SPD_HI|ASYNC_SPD_VHI|ASYNC_SPD_SHI)
 
-#ifndef _KERNEL_
+#ifndef __KERNEL__
 /* These flags are no longer used (and were always masked from userspace) */
 #define ASYNC_INITIALIZED	(1U << ASYNCB_INITIALIZED)
 #define ASYNC_NORMAL_ACTIVE	(1U << ASYNCB_NORMAL_ACTIVE)