powerpc/e6500: hw tablewalk: fix recursive tlb lock on cpu 0

Commit 82d86de2 "TLB lock recursive"
introduced a bug whereby cpu 0 uses the same value for "lock held" as
is used to indicate that the lock is free.  This means that cpu 1 can
acquire the lock whenever it wants, regardless of whether cpu 0 has it
locked, which in turn means we can get duplicate TLB entries.

Add one to the CPU value to ensure we do not use zero as a "lock held"
value.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Reported-by: Ed Swarthout <ed.swarthout@freescale.com>