Staging: hv: hv_mouse: fix up camelcase use for enum pipe_prot_msg_type in structures

It's a type, so call it that.

Cc: Hank Janssen <hjanssen@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>