MIPS: Remove no-op/identity casts

Clean up instances of casts to the type that a value already has, since
they are effectively no-ops and only serve to complicate the code.

This is the result of the following semantic patch:

  @identitycast@
  type T;
  T *A;
  @@
  -	(T *)(A)
  +	A

Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/19599/

arch/mips/kernel/traps.c

@@ -348,7 +348,7 @@ static void __show_regs(const struct pt_regs *regs)
  */
 void show_regs(struct pt_regs *regs)
 {
-	__show_regs((struct pt_regs *)regs);
+	__show_regs(regs);
 	dump_stack();
 }