clk: zx: fix pointer case warnings

The zx296718 clock driver has a creative way of assigning the register
values for each clock, by initializing an __iomem pointer to an
offset and then later adding the base (from ioremap) on top
with a cast to u64. This fail on all 32-bit architectures during
compile testing:

drivers/clk/zte/clk-zx296718.c: In function 'top_clocks_init':
drivers/clk/zte/clk-zx296718.c:554:35: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
   zx296718_pll_clk[i].reg_base += (u64)reg_base;
drivers/clk/zte/clk-zx296718.c:579:29: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
drivers/clk/zte/clk-zx296718.c:592:31: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]

It would be nice to avoid all the casts, but I decided to simply
shut up the warnings by changing the type from u64 to uintptr_t,
which does the right thing in practice.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: ca023328 ("clk: zx: register ZX296718 clocks")
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>