fbdev: omapfb: Add missing error check for clk_get()

fbdev: omapfb: Add missing error check for clk_get()

The hwa742_init() function did not check the return value of clk_get().
This could lead to dereferencing an error pointer in subsequent clock
operations, potentially causing a kernel crash.

Fix this by adding a missing error check and ensuring proper clock
resource cleanup on failure and driver removal.

Signed-off-by: Chen Ni <nichen@iscas.ac.cn>
Signed-off-by: Helge Deller <deller@gmx.de>