lrdp-v2: Use 'rb' mode when opening DDR files

Calling read_byte() on windows may return the empty string '' prior
to the end of the file without opening the file in 'rb' mode.

The 'rb' mode was removed by
commit 5743b613
("lrdp-v2: ramdump: Fix autoparse for some targets.")

Change-Id: Ibea608112400c06a9adc6f1fd3b4842a87717846