Update datatypes.py - fixed range for ChargingProfileEntryMaxPower

[shalinnijel2]

This is fix for the issue mentioned here:
#89
Error seen:

pydantic.error_wrappers.ValidationError: 1 validation error for ProfileEntryDetails
ChargingProfileMaxPower
ensure this value is less than or equal to 255 (type=value_error.number.not_le; limit_value=255)

The range specified for ChargingProfileMaxPower seems to be incorrect. The field type is PMaxType which is xs:short. This PR updates the range to match that of p_max in PMaxScheduleEntry.

<xs:complexType name="ProfileEntryType">
  <xs:sequence>
    <xs:element name="ChargingProfileEntryStart" type="xs:unsignedInt"/>
    <xs:element name="ChargingProfileEntryMaxPower" type="PMaxType"/>
  </xs:sequence>
</xs:complexType>

<xs:simpleType name="PMaxType">
  <xs:restriction base="xs:short"/>
</xs:simpleType>