fbdev: sh_mobile_lcdcfb: fix more error paths

This patch fixes the following two erroneous error paths:

hw_usecnt is allocated with a value of 0, therefore in an early error case,
calling sh_mobile_lcdc_clk_off() will wrongly conclude, that hw_usecnt has
already been incremented. Then sh_mobile_lcdc_runtime_suspend() will be called,
which will access uninitialised data fields and crash the kernel.

sh_mobile_lcdc_stop() can be called before framebuffer has been allocated, then
ch->info is NULL and dereferencing it will Oops too.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>