HV:fix 'missing for discarded return value' violations

Return value should be checked,fix it by add
"void" when the function return value is not used.

V1->V2:
    replace printf with pr_warn.
V2->V3:
    change the commit to make read easily.

Tracked-On:#861

Signed-off-by: Huihuang Shi <huihuang.shi@intel.com>
Reviewed-by: Jason Chen CJ <jason.cj.chen@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

hypervisor/arch/x86/guest/ucode.c

@@ -71,7 +71,7 @@ void acrn_update_ucode(struct vcpu *vcpu, uint64_t v)
 
 	msr_write(MSR_IA32_BIOS_UPDT_TRIG,
 			(uint64_t)ucode_ptr + sizeof(struct ucode_header));
-	get_microcode_version();
+	(void)get_microcode_version();
 
 	free(ucode_ptr);
 }