Fix variadic calls with float/double arguments
Fix variadic calls with float/double arguments

Problem was due to incorrect way to call C method ffi_prep_cif_var,
where third argument was passed as total number of arguments instead of
fixed number of arguments

This fixes ruby-ffi on the ppc64el architecture, and should be harmless
on other architectures. This was tested at least on amd64 (x86_64) and
ppc64el.

Signed-off-by: Antonio Terceiro <9e4dabace4bf3e60d3d713b56a1c8e7e285b5f80@debian.org>

yghannam/ffi,MikaelSmith/ffi,sparkchaser/ffi,mvz/ffi,ferventcoder/ffi,tduehr/ffi,tduehr/ffi,yghannam/ffi,mvz/ffi,ffi/ffi,ferventcoder/ffi,mvz/ffi,mvz/ffi,yghannam/ffi,yghannam/ffi,tduehr/ffi,sparkchaser/ffi,majioa/ffi,majioa/ffi,MikaelSmith/ffi,sparkchaser/ffi,tduehr/ffi,sparkchaser/ffi,majioa/ffi,MikaelSmith/ffi,yghannam/ffi,ferventcoder/ffi,ffi/ffi,MikaelSmith/ffi,majioa/ffi,ferventcoder/ffi,ffi/ffi