staging: unisys: refactor CONTROLVM_MESSAGE_HEADER

This patch removes the typedef from CONTROLVM_MESSAGE_HEADER, using the
struct controlvm_message_header name directly instead. It fixes
CamelCase names and updates all references to changed names:

MessageSize => message_size
SegmentIndex => segment_index
CompletionStatus => completion_status
responseExpected => response_expected
testMessage => test_message
partialCompletion => partial_completion
writerInDiag => writer_in_diag
Flags => flags
Reserved => reserved
MessageHandle => message_handle
PayloadVmOffset => payload_vm_offset
PayloadMaxBytes => payload_max_bytes
PayloadBytes => payload_bytes

Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>