bios_table: pldm_bios_table_attr_entry_string_encode_check() values

Document the pre-conditions that lead to failures and their associated
error codes.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: Iff1891565edf96d2447527682b4db3464a009cf1
diff --git a/include/libpldm/bios_table.h b/include/libpldm/bios_table.h
index 0ec3671..d21a386 100644
--- a/include/libpldm/bios_table.h
+++ b/include/libpldm/bios_table.h
@@ -374,7 +374,10 @@
  *  @param[in] entry_length - Length of the buffer to create an entry
  *  @param[in] info - Pointer to an auxiliary structure @ref
  * pldm_bios_table_attr_entry_string_info
- *  @return pldm_completion_codes
+ *  @return PLDM_SUCCESS on success, PLDM_ERROR_INVALID_DATA if entry or info are NULL or info
+ *          contains logically inconsistent data, or PLDM_ERROR_INVALID_LENGTH if entry_length is
+ *          not sufficient to encode info. An appropriate value for entry_length can be determined
+ *          using @ref pldm_bios_table_attr_entry_string_encode_length
  */
 int pldm_bios_table_attr_entry_string_encode_check(
 	void *entry, size_t entry_length,