uml: pty channel tidying

Cleanup, mostly style violations.

Tidied the includes.

getmaster returns a real errno, which pty_open returns if there's a
problem.

The printks now have severity.

Changed os_* calls to call libc directly.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>