IpmiFeaturePkg: fix IpmiSendCommand response size in GetDeviceId function

It is required to reinitialize DataSize variable before subsequent
IpmiSendCommand calls. It is especially required after processing
IpmiSendCommand with IPMI_GET_BMC_EXECUTION_CONTEXT because it returns
only 2 bytes as a response. So to the next call of IpmiSendCommand with
IPMI_APP_GET_DEVICE_ID DataSize=2 will be passed. Probably this call will
fail because the expected size of returned data either 12 or 16 bytes
depending on IPMI version supported.

Signed-off-by: Mike Maslenkin <mike.maslenkin@gmail.com>
Cc: Isaac Oram <isaac.w.oram@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Isaac Oram <isaac.w.oram@intel.com>