pstore: Remove needless lock during console writes

Since the console writer does not use the preallocated crash dump buffer
any more, there is no reason to perform locking around it.

Fixes: 70ad35db

 ("pstore: Convert console write to use ->write_buf")
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>