ARC: Fix bogus gcc warning and micro-optimise TLB iteration loop

ARC: Fix bogus gcc warning and micro-optimise TLB iteration loop

------------------>8----------------------
arch/arc/mm/tlb.c: In function ‘do_tlb_overlap_fault’:
arch/arc/mm/tlb.c:688:13: warning: array subscript is above array bounds
[-Warray-bounds]
         (pd0[n] & PAGE_MASK)) {
             ^
------------------>8----------------------

While at it, remove the usless last iteration of outer loop when reading
a TLB SET for duplicate entries.

Suggested-by: Mischa Jonker <mjonker@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>