x86/microcode/AMD: Do not return error when microcode update is not necessary

[ Upstream commit b43dc4ab097859c24e2a6993119c927cffc856aa ]

After

  6f059e634dcd("x86/microcode: Clarify the late load logic"),

if the load is up-to-date, the AMD side returns UCODE_OK which leads to
load_late_locked() returning -EBADFD.

Handle UCODE_OK in the switch case to avoid this error.

  [ bp: Massage commit message. ]

Fixes: 6f059e634dcd ("x86/microcode: Clarify the late load logic")
Signed-off-by: Annie Li <jiayanli@google.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/20250430053424.77438-1-jiayanli@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

arch/x86/kernel/cpu/microcode/core.c

@@ -703,6 +703,8 @@ static int load_late_locked(void)
 		return load_late_stop_cpus(true);
 	case UCODE_NFOUND:
 		return -ENOENT;
+	case UCODE_OK:
+		return 0;
 	default:
 		return -EBADFD;
 	}