NDS32/BFD: Fix build error in `nds32_convert_32_to_16'

Fix:

cc1: warnings being treated as errors
.../bfd/elf32-nds32.c: In function 'nds32_convert_32_to_16':
.../bfd/elf32-nds32.c:6816: error: 'insn_type' may be used uninitialized in this function
make[4]: *** [elf32-nds32.lo] Error 1

seen with GCC 4.1.2 and 4.4.7.

	bfd/
	* elf32-nds32.c (nds32_convert_32_to_16): Preset `insn_type'.