iio: trx-rf: ad9088: fix __counted_by misuse in ad9088_clk_register()

[nunojsa]

clk_hw_onecell_data::hws is a flexible array annotated with __counted_by(num). Using hws[num++] to append clocks is, in theory, correct from a sequence point perspective (the post-increment in a subscript is well-defined in C), but it triggers -Wsequence-point warnings with recent GCC versions. More importantly, it violates the __counted_by contract: the array is accessed at index num before the counter is incremented, triggering runtime UBSAN bounds checks.

Fix this by indexing hws with the source enum directly (which already indexes into phy->clks[]) and setting clk_data->num once upfront in ad9088_probe().

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