Fix boot_path Path loading

[petermm]

the boot path is a charlist eg erlang "".

AtomVM/libs/esp32boot/esp32init.erl

Line 86 in ed48c7c

"/dev/partition/by-name/main.avm";

But storing it in nvs with nvs_put_binary, means it's stored as a binary.

minimal fix.

eg this code now works:

  def start do
    case :esp.nvs_get_binary(:atomvm, :boot_path) do
      :undefined ->
        :esp.nvs_put_binary(:atomvm, :boot_path, "/dev/partition/by-name/main.avm")
        :timer.sleep(500)
        :esp.restart()

      "/dev/partition/by-name/main.avm" ->
        IO.inspect("boot_path already set")

      other ->
        IO.inspect("boot_path: #{other}")
    end
 end

would crash before with badarg, on the second boot with boot_path set.

These changes are made under both the "Apache 2.0" and the "GNU Lesser General
Public License 2.1 or later" license terms (dual license).

SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later