hv: fixed compiling warning

removed some unnecessary variables and functions.

v1-->v2:
   Replace div-by-zero with an inline ASM code

Signed-off-by: Mingqiang Chi <mingqiang.chi@intel.com>
Acked-by: Anthony Xu <anthony.xu@intel.com>

hypervisor/boot/acpi.c

@@ -115,12 +115,12 @@ biosacpi_search_rsdp(char *base, int length)
 		if (strncmp(rsdp->signature, ACPI_SIG_RSDP,
 				strnlen_s(ACPI_SIG_RSDP, 8)) == 0) {
 			cp = (uint8_t *)rsdp;
-			sum = NULL;
+			sum = 0U;
 			for (idx = 0; idx < RSDP_CHECKSUM_LENGTH; idx++) {
 				sum += *(cp + idx);
 			}
 
-			if (sum != NULL) {
+			if (sum != 0U) {
 				continue;
 			}