Shrink TIF_WORK_MASK so that it will fit in the 12-bit signed immediate
operand field of an ANDI instruction.

Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>