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

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.

Fixes: 980cd426a257 ("staging: rtl8723bs: replace rtw_zmalloc() with kzalloc()")
Cc: stable <stable@kernel.org>
Signed-off-by: Shyam Sunder Reddy Padira <shyamsunderreddypadira@gmail.com>
Reviewed-by: Dan Carpenter <error27@gmail.com>
Link: https://patch.msgid.link/20260414071308.4781-2-shyamsunderreddypadira@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>