Make Blockstore::get_data_shreds_for_slot() return type consistent

[steviez]

Problem

We have several other functions that return data shreds; however, these other functions map shred::Error to BlockstoreError. The other functions being:

solana/ledger/src/blockstore.rs

Line 1629 in cec6b86

pub fn get_data_shred(&self, slot: Slot, index: u64) -> Result<Option<Vec<u8>>> {

and

solana/ledger/src/blockstore.rs

Lines 2937 to 2943 in cec6b86

	pub fn get_entries_in_data_block(
	&self,
	slot: Slot,
	start_index: u32,
	end_index: u32,
	slot_meta: Option<&SlotMeta>,
	) -> Result<Vec<Entry>> {

The second one actually returns a Vec<Entry>, but the point stands that the return type of the function is Result<T, BlockstoreError>.

Summary of Changes

Make this function consistent with those and map the error.

Broke this out as cleanup from another PR

[codecov]

Codecov Report

Merging #32460 (2345f56) into master (0a1e641) will increase coverage by 0.0%.
The diff coverage is 57.1%.

@@           Coverage Diff           @@
##           master   #32460   +/-   ##
=======================================
  Coverage    82.1%    82.1%           
=======================================
  Files         778      778           
  Lines      210093   210098    +5     
=======================================
+ Hits       172545   172603   +58     
+ Misses      37548    37495   -53     

[jbiseda]

Looks good, one cleanup comment.

[jbiseda]

LGTM!