clk: ingenic: Remove set but not used variable 'enable'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/clk/ingenic/cgu.c: In function 'ingenic_pll_recalc_rate':
drivers/clk/ingenic/cgu.c:86:15: warning:
 variable 'enable' set but not used [-Wunused-but-set-variable]

It's not used after commit ab27eb4b ("clk: ingenic: Add code to
enable/disable PLLs")

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>