rtt: fix cb not found when the first character of the cb_id was not i…

…n the memory of this read (#1729)

pyocd/debug/rtt.py

@@ -426,6 +426,7 @@ def __init__(self, target: SoCTarget, address: int = None,
 
     def _find_control_block(self) -> Optional[int]:
         addr: int = self._cb_search_address & ~0x3
+        search_addr: int = addr
         search_size: int  = self._cb_search_size_bytes
         if search_size < len(self._control_block_id):
             search_size = len(self._control_block_id)
@@ -435,7 +436,7 @@ def _find_control_block(self) -> Optional[int]:
 
         while search_size:
             read_size = min(search_size, 32)
-            data = self.target.read_memory_block8(addr, read_size)
+            data = self.target.read_memory_block8(search_addr, read_size)
 
             if not data:
                 break
@@ -454,6 +455,8 @@ def _find_control_block(self) -> Optional[int]:
             if offset == id_len:
                 break
 
+            search_addr += read_size
+
         return addr if offset == id_len else None
 
     def start(self):