hw/core/cpu: gdb_arch_name string should not be freed

The documentation for the CPUClass::gdb_arch_name method claims that
the returned string should be freed with g_free().  This is not
correct: in commit a650683871 we changed this method to
instead return a simple constant string, but forgot to update
the documentation.

Make the documentation match the new semantics.

Fixes: a650683871 ("hw/core/cpu: Return static value with gdb_arch_name()")
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20250317142819.900029-2-peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

include/hw/core/cpu.h

@@ -134,7 +134,8 @@ struct SysemuCPUOps;
  * @gdb_stop_before_watchpoint: Indicates whether GDB expects the CPU to stop
  *           before the insn which triggers a watchpoint rather than after it.
  * @gdb_arch_name: Optional callback that returns the architecture name known
- * to GDB. The caller must free the returned string with g_free.
+ * to GDB. The returned value is expected to be a simple constant string:
+ * the caller will not g_free() it.
  * @disas_set_info: Setup architecture specific components of disassembly info
  * @adjust_watchpoint_address: Perform a target-specific adjustment to an
  * address before attempting to match it against watchpoints.