qemu/osdep: Reword qemu_get_exec_dir() documentation

This comment is confuse, reword it a bit.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Michael Rolnik <mrolnik@gmail.com>
Tested-by: Michael Rolnik <mrolnik@gmail.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20200714164257.23330-3-f4bug@amsat.org>

include/qemu/osdep.h

@@ -588,7 +588,10 @@ char *qemu_get_local_state_pathname(const char *relative_pathname);
 void qemu_init_exec_dir(const char *argv0);
 
 /* Get the saved exec dir.
- * Caller needs to release the returned string by g_free() */
+ *
+ * The caller is responsible for releasing the value returned with g_free()
+ * after use.
+ */
 char *qemu_get_exec_dir(void);
 
 /**