ACPICA: Add a couple of casts to uthex.c

ACPICA commit 2ba5d3fdaa24d66d67694cbae6ec66971a7a67c1

Required in some environments.

Link: https://github.com/acpica/acpica/commit/2ba5d3fd
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/acpica/uthex.c

@@ -92,7 +92,8 @@ acpi_status acpi_ut_ascii_to_hex_byte(char *two_ascii_chars, u8 *return_byte)
 
 	/* Both ASCII characters must be valid hex digits */
 
-	if (!isxdigit(two_ascii_chars[0]) || !isxdigit(two_ascii_chars[1])) {
+	if (!isxdigit((int)two_ascii_chars[0]) ||
+	    !isxdigit((int)two_ascii_chars[1])) {
 		return (AE_BAD_HEX_CONSTANT);
 	}