[PARISC] fix personality flag check in copy_thread()

Directly comparing task_struct->personality against PER_* is not fully
correct, as it doesn't take flags potentially stored in top three bytes
into account.

Analogically, directly forcefully setting personality to PER_LINUX32 or
PER_LINUX discards any flags stored in the top three bytes.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>