drm/panfrost: Fix missing clk_disable_unprepare() on error in panfrost_clk_init()

Fix the missing clk_disable_unprepare() before return
from panfrost_clk_init() in the error handling case.

Fixes: b681af0b ("drm: panfrost: add optional bus_clock")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210608143856.4154766-1-weiyongjun1@huawei.com