clk: zynqmp: Fix memory allocation in zynqmp_clk_setup

Fix memory allocation and use struct_size() in kzalloc(). This also
fixes the allocation size to be correct, and smaller, because before we
were allocating a bunch of sizeof(struct clk_hw_onecell_data) structures
for each struct clk_hw we needed.

Fixes: 3fde0e16 ("drivers: clk: Add ZynqMP clock driver")
Cc: stable@vger.kernel.org
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: Michal Simek <michal.simek@xilinx.com>
[sboyd@kernel.org: Expand commit text]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>