x86/microcode/amd: Tone down printk(), don't treat a missing firmware file as an error

Do it the same way as done in microcode_intel.c: use pr_debug()
for missing firmware files.

There seem to be CPUs out there for which no microcode update
has been submitted to kernel-firmware repo yet resulting in
scary sounding error messages in dmesg:

  microcode: failed to load file amd-ucode/microcode_amd_fam16h.bin
Signed-off-by: Thomas Renninger <trenn@suse.de>
Acked-by: Borislav Petkov <bp@suse.de>
Cc: <stable@kernel.org>
Link: http://lkml.kernel.org/r/1384274383-43510-1-git-send-email-trenn@suse.deSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/microcode_amd.c

@@ -431,7 +431,7 @@ static enum ucode_state request_microcode_amd(int cpu, struct device *device,
 		snprintf(fw_name, sizeof(fw_name), "amd-ucode/microcode_amd_fam%.2xh.bin", c->x86);
 
 	if (request_firmware(&fw, (const char *)fw_name, device)) {
-		pr_err("failed to load file %s\n", fw_name);
+		pr_debug("failed to load file %s\n", fw_name);
 		goto out;
 	}