MIPS: DEC: Remove do_IRQ() call indirection

[ Upstream commit 35554ea ]

As from commit 8f99a16 ("MIPS: Tracing: Add IRQENTRY_EXIT section
for MIPS") do_IRQ() is not a macro anymore and can be invoked directly
from assembly code, as a tail call.  Remove the dec_irq_dispatch() stub
then and the indirection previously introduced with commit 187933f
("[MIPS] do_IRQ cleanup"), improving performance by reducing the number
of control flow changes and the overall instruction count, while fixing
a compiler's complaint about a missing prototype for said stub:

arch/mips/dec/setup.c:780:25: warning: no previous prototype for 'dec_irq_dispatch' [-Wmissing-prototypes]
  780 | asmlinkage unsigned int dec_irq_dispatch(unsigned int irq)
      |                         ^~~~~~~~~~~~~~~~

(which gets promoted to a compilation error with CONFIG_WERROR).

Fixes: 8f99a16 ("MIPS: Tracing: Add IRQENTRY_EXIT section for MIPS")
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: maciej-w-rozycki

arch/mips/dec/int-handler.S

@@ -277,7 +277,7 @@
 		 srlv	t3,t1,t2
 
 handle_it:
-		j	dec_irq_dispatch
+		j	do_IRQ
 		 nop
 
 #if defined(CONFIG_32BIT) && defined(CONFIG_MIPS_FP_SUPPORT)

arch/mips/dec/setup.c

@@ -776,9 +776,3 @@ void __init arch_init_irq(void)
 			pr_err("Failed to register halt interrupt\n");
 	}
 }
-
-asmlinkage unsigned int dec_irq_dispatch(unsigned int irq)
-{
-	do_IRQ(irq);
-	return 0;
-}