RTT control block search code malfunction

[elfmimi]

RTT control block search code functions incorrectly in certain cases.

A typical case is when the control block ID string is located across a 32-byte boundary.

error message for rtt subcommand:

0001919 C Control block not found [main]

error message for gdbserver subcommand, shown in gdb side:

Error: Control block not found

workaround:

try changing the base address by offset of 16 bytes. that is, one out of the following two should succeed.
pyocd rtt --target cortex_m -a 0x20000000 -s 0x10000
pyocd rtt --target cortex_m -a 0x20000010 -s 0x10000

or force 16-byte alignment for RTT control block.