powerpc/mm/radix: Fix always false comparison against MMU_NO_CONTEXT

In commit 9690c157 ("powerpc/mm/radix: Fix always false comparison
against MMU_NO_CONTEXT") an issue was discovered where `mm->context.id` was
being truncated to an `unsigned int`, while the PID is actually an
`unsigned long`. Update the earlier patch by fixing one remaining
occurrence. Discovered during a compilation with W=1:

  arch/powerpc/mm/tlb-radix.c:702:19: error: comparison is always false due to limited range of data type [-Werror=type-limits]
Signed-off-by: Mathieu Malaterre <malat@debian.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/mm/tlb-radix.c

@@ -706,7 +706,7 @@ void radix__flush_tlb_pte_p9_dd1(unsigned long old_pte, struct mm_struct *mm,
 #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
 extern void radix_kvm_prefetch_workaround(struct mm_struct *mm)
 {
-	unsigned int pid = mm->context.id;
+	unsigned long pid = mm->context.id;
 
 	if (unlikely(pid == MMU_NO_CONTEXT))
 		return;