clk: boston: fix possible memory leak in clk_boston_setup()

Smatch report warnings:
drivers/clk/imgtec/clk-boston.c:76 clk_boston_setup() warn: possible memory leak of 'onecell'
drivers/clk/imgtec/clk-boston.c:83 clk_boston_setup() warn: possible memory leak of 'onecell'
drivers/clk/imgtec/clk-boston.c:90 clk_boston_setup() warn: possible memory leak of 'onecell'

'onecell' is malloced in clk_boston_setup(), but not be freed
before leaving from the error handling cases.

Signed-off-by: Yi Wang <wang.yi59@zte.com.cn>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>