clk: socfpga: fix iomem pointer cast on 64-bit

Pointers should be cast with uintptr_t instead of integer.  This fixes
warning when compile testing on ARM64:

  drivers/clk/socfpga/clk-gate.c: In function ‘socfpga_clk_recalc_rate’:
  drivers/clk/socfpga/clk-gate.c:102:7: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]

Fixes: b7cec13f ("clk: socfpga: Look for the GPIO_DB_CLK by its offset")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Acked-by: Dinh Nguyen <dinguyen@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>