MdeModulePkg/DxeCore: Fixed Interface returned by CoreOpenProtocol

MdeModulePkg/DxeCore: Fixed Interface returned by CoreOpenProtocol

Change since v3:
1) Fixed issue when Attributes = EFI_OPEN_PROTOCOL_TEST_PROTOCOL
and Inteface = NULL case. [Reported by:star.zeng at intel.com]

Change Since v2:
1) Modified to use EFI_ERROR to get status code

Change since v1:
1) Fixed typo protocal to protocol
2) Fixed coding style

Modified source code to update Interface as per spec.
1) In case of Protocol is un-supported, interface should be returned NULL.
2) In case of any error, interface should not be modified.
3) In case of Test Protocol, interface is optional.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Amit Kumar <amit.ak@samsung.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>