rtc: ac100: Assign .num before accessing .hws

Commit f316cdff8d67 ("clk: Annotate struct clk_hw_onecell_data with
__counted_by") annotated the hws member of 'struct clk_hw_onecell_data'
with __counted_by, which informs the bounds sanitizer (UBSAN_BOUNDS)
about the number of elements in .hws[], so that it can warn when .hws[]
is accessed out of bounds. As noted in that change, the __counted_by
member must be initialized with the number of elements before the first
array access happens, otherwise there will be a warning from each access
prior to the initialization because the number of elements is zero.
This occurs in ac100_rtc_register_clks() due to .num being assigned only
after every clkout clock has been stored in .hws[]. With
CONFIG_UBSAN_BOUNDS and a compiler that implements __counted_by (GCC
15.1+ or Clang 20.1+), this triggers an array-index-out-of-bounds report
during probe, and with CONFIG_UBSAN_TRAP the first store traps.

Initialize .num with AC100_CLKOUT_NUM, the number of elements .hws[] was
allocated with, right after the allocation. That is the value the loop
counter ends up at on the success path anyway, so the provider's
behaviour is unchanged.

Cc: stable@vger.kernel.org
Fixes: f316cdff8d67 ("clk: Annotate struct clk_hw_onecell_data with __counted_by")
Assisted-by: LLM
Signed-off-by: Aamir Ahmed <elb12345@hotmail.co.uk>
Reviewed-by: Chen-Yu Tsai <wens@kernel.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://patch.msgid.link/AS8P251MB00013E724A77A355668B6CCEC8B42@AS8P251MB0001.EURP251.PROD.OUTLOOK.COM
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>