clk: meson: Fix meson_clk_register_clks() signature type mismatch

As preparation for arm64 based mesongxbb, which pulls in this code once
enabling ARCH_MESON, fix a size_t vs. unsigned int type mismatch.
The loop uses a local unsigned int variable, so adopt that type,
matching the header.

Fixes: 7a29a869 ("clk: meson: Add support for Meson clock controller")
Signed-off-by: Andreas Färber <afaerber@suse.de>
Acked-by: Carlo Caione <carlo@endlessm.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>