fix pda error

[chen4903]

fix this error

mismatched types
expected enum `std::result::Result<(), _>`
   found enum `std::result::Result<Return<u64>, _>`rustc[Click for full compiler diagnostic](rust-analyzer-diagnostics-view:/diagnostic%20message%20[0]?0#file:///Users/levi/code/web3/solana/puppet/programs/puppet-master/src/lib.rs)
lib.rs(12, 76): expected `std::result::Result<(), anchor_lang::error::Error>` because of return type

[acheroncrypto]

It looks like we give 2 examples of puppet::set_data:

anchor-book/src/anchor_in_depth/CPIs.md

Line 29 in 1abc5a5

pub fn set_data(ctx: Context<SetData>, data: u64) -> Result<()> {

anchor-book/src/anchor_in_depth/CPIs.md

Line 378 in 1abc5a5

pub fn set_data(ctx: Context<SetData>, data: u64) -> Result<u64> {

Therefore, it certainly makes sense for the code to work both ways here. Thank you!