md/raid5: validate payload size before accessing journal metadata

In the Linux kernel, the following vulnerability has been resolved: md/raid5: validate payload size before accessing journal metadata r5c_recovery_analyze_meta_block() and r5l_recovery_verify_data_checksum_for_mb() iterate over payloads in a journal metadata block using on-disk payload size fields without validating them against the remaining space in the metadata block. A corrupted journal contains payload sizes extending beyond the PAGE_SIZE boundary can cause out-of-bounds reads when accessing payload fields or computing offsets. Add bounds validation for each payload type to ensure the full payload fits within meta_size before processing.