staging: rtl8723bs: fix memory leak on failure path

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

staging: rtl8723bs: fix memory leak on failure path

cfg80211_inform_bss_frame() may return NULL on failure. In that case,

the allocated buffer 'buf' is not freed and the function returns early,

leading to potential memory leak.

Fix this by ensuring that 'buf' is freed on both success and failure paths.