target/arc: fix clang static analyzer warnings

target/arc: fix clang static analyzer warnings

Fixes:
* Removed typo in *bitfields initializations.
* Removed potentional memory leak allocating
  reg_data_type_struct_field/reg_data_type_flags_field objects.
* Initialize buffers with "0" before usage in buf_set_u32().
* Removed memory leak in jim_arc_add_reg().

Change-Id: Iefde57cd4a48c4f3350c376475df8642607f52ff
Signed-off-by: Evgeniy Didin <didin@synopsys.com>
Reviewed-on: http://openocd.zylin.com/5480
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Tested-by: jenkins
Reviewed-by: Oleksij Rempel <linux@rempel-privat.de>