clear offset when crossing flash pages

When doing a flash read that crosses pages, clear the offset once
the first page is read.

Author: tlyu

src/jtag2rw.cc

@@ -193,6 +193,7 @@ uchar *jtag2::jtagRead(unsigned long addr, unsigned int numBytes)
 
 	    numBytes -= chunksize;
 	    targetOffset += chunksize;
+	    offset = 0;
 
 	    chunksize = numBytes > pageSize? pageSize: numBytes;
 	    pageAddr += pageSize;