staging: rtl8723bs: os_dep: avoid NULL pointer dereference in rtw_cbuf_alloc

In the Linux kernel, the following vulnerability has been resolved: staging: rtl8723bs: os_dep: avoid NULL pointer dereference in rtw_cbuf_alloc The return value of kzalloc_flex() is used without ensuring that the allocation succeeded, and the pointer is dereferenced unconditionally. Guard the access to the allocated structure to avoid a potential NULL pointer dereference if the allocation fails.