powerpc/64s: Reconnect tlb_flush() to hash__tlb_flush()

Commit baf1ed24b2 ("powerpc/mm: Remove empty hash__ functions")
removed some empty hash MMU flushing routines, but got a bit overeager
and also removed the call to hash__tlb_flush() from tlb_flush().

In regular use this doesn't lead to any noticable breakage, which is a
little concerning. Presumably there are flushes happening via other
paths such as arch_leave_lazy_mmu_mode(), and/or a bit of luck.

Fix it by reinstating the call to hash__tlb_flush().

Fixes: baf1ed24b2 ("powerpc/mm: Remove empty hash__ functions")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230131111407.806770-1-mpe@ellerman.id.au

arch/powerpc/include/asm/book3s/64/tlbflush.h

@@ -97,6 +97,8 @@ static inline void tlb_flush(struct mmu_gather *tlb)
 {
 	if (radix_enabled())
 		radix__tlb_flush(tlb);
+
+	return hash__tlb_flush(tlb);
 }
 
 #ifdef CONFIG_SMP