x86/srso: Fix SBPB enablement for (possible) future fixed HW

Make the SBPB check more robust against the (possible) case where future
HW has SRSO fixed but doesn't have the SRSO_NO bit set.

Fixes: 1b5277c0 ("x86/srso: Add SRSO_NO support")
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/cee5050db750b391c9f35f5334f8ff40e66c01b9.1693889988.git.jpoimboe@kernel.org

arch/x86/kernel/cpu/bugs.c

@@ -2496,7 +2496,7 @@ static void __init srso_select_mitigation(void)
 	pr_info("%s%s\n", srso_strings[srso_mitigation], (has_microcode ? "" : ", no microcode"));
 
 pred_cmd:
-	if ((boot_cpu_has(X86_FEATURE_SRSO_NO) || srso_cmd == SRSO_CMD_OFF) &&
+	if ((!boot_cpu_has_bug(X86_BUG_SRSO) || srso_cmd == SRSO_CMD_OFF) &&
 	     boot_cpu_has(X86_FEATURE_SBPB))
 		x86_pred_cmd = PRED_CMD_SBPB;
 }