fix(spl): modify program to avoid missing function issue

[Stevengre]

No description provided.

[jberthold]

LGTM as a work-around (behaviour is equivalent).
A similar change was applied earlier in

solana-token/interface/src/instruction.rs

Lines 498 to 502 in 6ce7407

	let amount_bytes: [u8; 8] = rest
	.get(..8)
	.and_then(|slice| slice.try_into().ok())
	.ok_or(InvalidInstruction)?;
	let amount = u64::from_le_bytes(amount_bytes);