package/prosody: use correct bit32 package

According to https://prosody.im/doc/depends#bitop the correct bitop
package to use with prosody for Lua 5.1 is:
https://luarocks.org/modules/siffiejoe/bit32



As such replace BR2_PACKAGE_LUABITOP with BR2_PACKAGE_LUA_BIT32

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>