clk: mvebu: armada-37xx-periph: fix __iomem casts in structure init

There are a number of casts to "void __iomem *" in the initialsation
of the driver's clk information. Fix this by adding a helper macro
for the cast.

Silences a number of sparse warnings:

drivers/clk/mvebu/armada-37xx-periph.c:254:1: warning: incorrect type in initializer (different address spaces)
drivers/clk/mvebu/armada-37xx-periph.c:254:1: expected void [noderef] __iomem *reg
drivers/clk/mvebu/armada-37xx-periph.c:254:1: got void *
drivers/clk/mvebu/armada-37xx-periph.c:254:1: warning: incorrect type in initializer (different address spaces)
drivers/clk/mvebu/armada-37xx-periph.c:254:1: expected void [noderef] __iomem *reg1
drivers/clk/mvebu/armada-37xx-periph.c:254:1: got void *
drivers/clk/mvebu/armada-37xx-periph.c:254:1: warning: incorrect type in initializer (different address spaces)
drivers/clk/mvebu/armada-37xx-periph.c:254:1: expected void [noderef] __iomem *reg2
drivers/clk/mvebu/armada-37xx-periph.c:254:1: got void *
drivers/clk/mvebu/armada-37xx-periph.c:255:1: warning: incorrect type in initializer (different address spaces)
drivers/clk/mvebu/armada-37xx-periph.c:255:1: expected void [noderef] __iomem *reg
drivers/clk/mvebu/armada-37xx-periph.c:255:1: got void *
...

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Reviewed-by: Brian Masney <bmasney@redhat.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>