[MIPS] DECstation: Fix irq handling

When I post a patch (commit f431baa5),
I just tried to not change behavior of existing codes, but it seems
dec/int-handler.S had been broken since its previous commit
937a8015.

The caller of plat_irq_dispatch do setup/restore TI_REGS($28), so
dec's plat_irq_dispatch should not do it, and there is no need to
adjust RA.
Signed-off-by: NAtsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/dec/int-handler.S

@@ -264,9 +264,6 @@
 		 srlv	t3,t1,t2
 
 handle_it:
-		LONG_L	s0, TI_REGS($28)
-		LONG_S	sp, TI_REGS($28)
-		PTR_LA	ra, ret_from_irq
 		j	dec_irq_dispatch
 		 nop
 
@@ -277,7 +274,6 @@ fpu:
 #endif
 
 spurious:
-		PTR_LA	ra, _ret_from_irq
 		j	spurious_interrupt
 		 nop
 		END(plat_irq_dispatch)