This variable is no longer used and the compiler rightly complains that
it should be removed. Drop it to silence the following:
drivers/clk/renesas/rcar-gen3-cpg.c: In function 'cpg_sd_clk_register':
drivers/clk/renesas/rcar-gen3-cpg.c:386:15: warning: unused variable 'i' [-Wunused-variable]
unsigned int i;