kernel/fork.c: simplify copy_mm()

All this can happen without a single goto.

Link: https://lkml.kernel.org/r/2072685.XptgVkyDqn@devpool47


Signed-off-by: Rolf Eike Beer <eb@emlix.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>