video: fbdev: simplefb: Check before clk_put() not needed

clk_put() already checks the clk ptr using !clk and IS_ERR()
so there is no need to check it again before calling it.

Signed-off-by: Yihao Han <hanyihao@vivo.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Helge Deller <deller@gmx.de>