staging: unisys: visorbus: Have unisys_vmcall return Linux error instead of VMCALL error

The function unisys_vmcall was returning VMCALL specific errors and the
calling code was ignoring which error was actually returned. Instead we
should be mapping the VMCALL error into a proper Linux error and then
returning that, since we now have an error we know what to do with, we
don't have to drop it but we can send it up the stack.

Signed-off-by: David Kershner <david.kershner@unisys.com>
Reviewed-by: Reviewed-by: Tim Sell <timothy.sell@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>