bios_table: pldm_bios_table_attr_entry_enum_decode_def_num_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: I84864c2541e0d6e6f67a7a36273ce08ac915ca34
diff --git a/include/libpldm/bios_table.h b/include/libpldm/bios_table.h
index f6056da..533a480 100644
--- a/include/libpldm/bios_table.h
+++ b/include/libpldm/bios_table.h
@@ -286,7 +286,8 @@
  * validity of the parameters
  *  @param[in] entry - Pointer to bios attribute table entry
  *  @param[out] def_num - Pointer to total number of default values
- *  @return pldm_completion_codes
+ *  @return PLDM_SUCCESS on success, otherwise PLDM_ERROR_INVALID_DATA if entry or def_num are NULL,
+ *          or entry is not of type PLDM_BIOS_ENUMERATION.
  */
 int pldm_bios_table_attr_entry_enum_decode_def_num_check(
 	const struct pldm_bios_attr_table_entry *entry, uint8_t *def_num);