clk: axi-clkgen: use devm_platform_ioremap_resource() short-hand

No major functional change. Noticed while checking the driver code that
this could be used.
Saves two lines.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20210201151245.21845-5-alexandru.ardelean@analog.com


Signed-off-by: Stephen Boyd <sboyd@kernel.org>