clk: rockchip: rk3528: add slab.h header include

The newly added GRF types introduced kzalloc usage into the rk3528.
At least for the similar rk3576 driver, the kernel-test-robot reported the
missing prototype, which warranted adding a slab.h include.

While it did not complain about the rk3528, so the header might be included
"accidentially" right now, add a real include to make sure we keep it
included in the future.

Fixes: 306d2f5 ("clk: rockchip: rk3528: Add SD/SDIO tuning clocks in GRF region")
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20250515082652.2503063-2-heiko@sntech.de

Author: mmind

drivers/clk/rockchip/clk-rk3528.c

@@ -12,6 +12,7 @@
 #include <linux/platform_device.h>
 #include <linux/mfd/syscon.h>
 #include <linux/minmax.h>
+#include <linux/slab.h>
 
 #include <dt-bindings/clock/rockchip,rk3528-cru.h>