uboot-phytec

Makefile: Don't shadow actual error when compile ASL

If ASL compiler failed by any reason do not produce output C file.
Otherwise sequential run of make will shadow the actual error in ASL,
i.e.

  CC      board/intel/edison/dsdt.o
board/intel/edison/dsdt.c:1:1: error: unterminated comment
 /*

and user has to remove dsdt.c and run make in order to see the error again.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>