microcode: Add error msg in case `intel_microcode_find()` return NULL

This patch adds an error msg if intel_microcode_find() is unable to
find a microcode for the CPU SKU.

TEST=Able to see the error msg in coreboot serial log in case packed
with wrong microcode binary.

Signed-off-by: Subrata Banik <subratabanik@google.com>
Change-Id: Ib4865575a44d2c8c6c3a20c2823a546d8f261e52
Reviewed-on: https://review.coreboot.org/c/coreboot/+/65285
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/cpu/intel/microcode/microcode.c

@@ -94,8 +94,10 @@ void intel_microcode_load_unlocked(const void *microcode_patch)
 	u32 current_rev;
 	const struct microcode *m = microcode_patch;
 
-	if (!m)
+	if (!m) {
+		printk(BIOS_ERR, "microcode: failed because no ucode was found\n");
 		return;
+	}
 
 	current_rev = read_microcode_rev();