Coverity fixes in arch/intel.c

CID 703167 (#1 of 1): Missing parentheses (CONSTANT_EXPRESSION_RESULT)missing_parentheses: !instance->os_type == VMI_OS_WINDOWS is always false regardless of the values of its operands. This occurs as the logical operand of if.
CID 1237204 (#1 of 1): Unchecked return value (CHECKED_RETURN)2. check_return: Calling vmi_read_64_pa without checking return value (as is done elsewhere 14 out of 15 times).
CID 1237206 (#1 of 1): Logically dead code (DEADCODE)dead_error_line: Execution cannot reach this statement: return;.