Hip: Supress transformation warning in softmax.cu

[IMbackK]

loops with bounds not known at compile time indeed can not be unrolled.

when ncols_template == 0, the bounds of the loop are not constexpr, thus llvm cant unroll the loops here. This causes annoying repeating warnings:

llama.cpp/ggml/src/ggml-cuda/softmax.cu:17:24: warning: loop not unrolled: the optimizer was unable to perform the requested transformation; the transformation might be disabled or specified as part of an unsupported transformation ordering [-Wpass-failed=transform-warning]

so lets suppress the this warning in this position as we know these loops cant be unrolled but we want to keep the pragma as it unrolls the loop just fine in the ncols_template != 0 case.

[JohannesGaessler]

Please add a brief comment explaining this to the code.

[IMbackK]

done

[JohannesGaessler]

CI didn't finish yet but I would be very surprised if a warning suppression were to cause issues.