powerpc: copy_thread don't set PPR in user interrupt frame regs

syscalls do not set the PPR field in their interrupt frame and
return from syscall always sets the default PPR for userspace,
so setting the value in the ret_from_fork frame is not necessary
and mildly inconsistent. Remove it.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230325122904.2375060-9-npiggin@gmail.com

arch/powerpc/kernel/process.c

@@ -1812,11 +1812,6 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 				f = ret_from_fork;
 		}
 
-#ifdef CONFIG_PPC64
-		if (cpu_has_feature(CPU_FTR_HAS_PPR))
-			childregs->ppr = DEFAULT_PPR;
-#endif
-
 		childregs->msr &= ~(MSR_FP|MSR_VEC|MSR_VSX);
 		p->thread.regs = childregs;
 	}