powerpc/lib: Fix emulate_step() std test

We should be checking that the instruction was stepped *and* that the
target register has the right value.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
[mpe: Write change log]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200226055302.1577954-1-npiggin@gmail.com

arch/powerpc/lib/test_emulate_step.c

@@ -160,7 +160,7 @@ static void __init test_std(void)
 
 	/* std r5, 0(r3) */
 	stepped = emulate_step(&regs, TEST_STD(5, 3, 0));
-	if (stepped == 1 || regs.gpr[5] == a)
+	if (stepped == 1 && regs.gpr[5] == a)
 		show_result("std", "PASS");
 	else
 		show_result("std", "FAIL");