mm/mempolicy.c: fix error handling in set_mempolicy and mbind.

mm/mempolicy.c: fix error handling in set_mempolicy and mbind.

In the case that compat_get_bitmap fails we do not want to copy the
bitmap to the user as it will contain uninitialized stack data and leak
sensitive data.

Bug 1971958

Signed-off-by: Chris Salls <salls@cs.ucsb.edu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Change-Id: I5b40ffb7f8d6b8c129e7b94f987346b52286502b
Reviewed-on: https://git-master.nvidia.com/r/1560690
GVS: Gerrit_Virtual_Submit
Reviewed-by: Hayden Du <haydend@nvidia.com>
Tested-by: Hayden Du <haydend@nvidia.com>
Reviewed-by: James Huang <jamehuang@nvidia.com>
Tested-by: James Huang <jamehuang@nvidia.com>