CVE-2022-50130: staging: fbtft: core: set smem_len before fb_deferred_io_init call

In the Linux kernel, the following vulnerability has been resolved:

staging: fbtft: core: set smemlen before fbdeferredioinit call

The fbtftframebufferalloc() calls fbdeferredioinit() before initializing info->fix.smemlen. It is set to zero by the framebufferalloc() function. It will trigger a WARNON() at the start of fbdeferredioinit() and the function will not do anything.