Workaround PPC backend bug in test for r346322.

It seems that the PPC backend croaks when lowering a call to a
function with an argument of type [2 x i32].

Just modify the type slightly to avoid this -- I wasn't actually
intending to stress test the backend...

llvm/lib/Target/PowerPC/PPCISelLowering.cpp:6172: llvm::SDValue llvm::PPCTargetLowering::LowerCall_64SVR4(...): Assertion `(!HasParameterArea || NumBytesActuallyUsed == ArgOffset) && "mismatch in size of parameter area"' failed.

llvm-svn: 346334