MIPS/ptrace: Update mips_get_syscall_arg's return type

clang warns:

arch/mips/include/asm/syscall.h:136:3: error: variable 'ret' is
uninitialized when used here [-Werror,-Wuninitialized]
ret |= mips_get_syscall_arg(args++, task, regs, i++);
^~~
arch/mips/include/asm/syscall.h:129:9: note: initialize the variable
'ret' to silence this warning
int ret;
^
= 0
1 error generated.

It's not wrong; however, it's not an issue in practice because ret is
only assigned to, not read from. ret could just be initialized to zero
but looking into it further, ret has been unused since it was first
added in 2012 so just get rid of it and update mips_get_syscall_arg's
return type since none of the return values are ever checked. If it is
ever needed again, this commit can be reverted and ret can be properly
initialized.

Fixes: c0ff3c53d4f9 ("MIPS: Enable HAVE_ARCH_TRACEHOOK.")
Link: https://github.com/ClangBuiltLinux/linux/issues/604
Signed-off-by: Nathan Chancellor <[e-mail]>
Signed-off-by: Paul Burton <[e-mail]>
Cc: Ralf Baechle <[e-mail]>
Cc: James Hogan <[e-mail]>
Cc: Nick Desaulniers <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]

arch/mips/include/asm/syscall.h

···
 		task_thread_info(task)->syscall = regs->regs[2];
 }
 
-static inline unsigned long mips_get_syscall_arg(unsigned long *arg,
+static inline void mips_get_syscall_arg(unsigned long *arg,
 	struct task_struct *task, struct pt_regs *regs, unsigned int n)
 {
 	unsigned long usp __maybe_unused = regs->regs[29];
···
 	case 0: case 1: case 2: case 3:
 		*arg = regs->regs[4 + n];
 
-		return 0;
+		return;
 
 #ifdef CONFIG_32BIT
 	case 4: case 5: case 6: case 7:
-		return get_user(*arg, (int *)usp + n);
+		get_user(*arg, (int *)usp + n);
+		return;
 #endif
 
 #ifdef CONFIG_64BIT
 	case 4: case 5: case 6: case 7:
 #ifdef CONFIG_MIPS32_O32
 		if (test_tsk_thread_flag(task, TIF_32BIT_REGS))
-			return get_user(*arg, (int *)usp + n);
+			get_user(*arg, (int *)usp + n);
 		else
 #endif
 			*arg = regs->regs[4 + n];
 
-		return 0;
+		return;
 #endif
 
 	default:
···
 {
 	unsigned int i = 0;
 	unsigned int n = 6;
-	int ret;
 
 	/* O32 ABI syscall() */
 	if (mips_syscall_is_indirect(task, regs))
 		i++;
 
 	while (n--)
-		ret |= mips_get_syscall_arg(args++, task, regs, i++);
-
-	/*
-	 * No way to communicate an error because this is a void function.
-	 */
-#if 0
-	return ret;
-#endif
+		mips_get_syscall_arg(args++, task, regs, i++);
 }
 
 extern const unsigned long sys_call_table[];