asm-generic/hyperv: Add missing function prototypes per -W1 warnings

Add two function prototypes for -W1 warnings generated by the
kernel test robot.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/1615402069-39462-1-git-send-email-mikelley@microsoft.com


Signed-off-by: Wei Liu <wei.liu@kernel.org>