powerpc/64e: Fix bogus usage of WARN_ONCE()

WARN_ONCE() takes a condition and a format string. We were passing a
constant string as the condition, and the function name as the format
string. It would work, but the message would be just the function name.

Fix it by just using WARN_ONCE() directly instead of if (x) WARN_ONCE().
Noticed-by: Geliang Tang <geliangtang@163.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/setup_64.c

@@ -113,14 +113,12 @@ void __init setup_tlb_core_data(void)
 		 * If we have threads, we need either tlbsrx.
 		 * or e6500 tablewalk mode, or else TLB handlers
 		 * will be racy and could produce duplicate entries.
+		 * Should we panic instead?
 		 */
-		if (smt_enabled_at_boot >= 2 &&
-		    !mmu_has_feature(MMU_FTR_USE_TLBRSRV) &&
-		    book3e_htw_mode != PPC_HTW_E6500) {
-			/* Should we panic instead? */
-			WARN_ONCE("%s: unsupported MMU configuration -- expect problems\n",
-				  __func__);
-		}
+		WARN_ONCE(smt_enabled_at_boot >= 2 &&
+			  !mmu_has_feature(MMU_FTR_USE_TLBRSRV) &&
+			  book3e_htw_mode != PPC_HTW_E6500,
+			  "%s: unsupported MMU configuration\n", __func__);
 	}
 }
 #endif