bnxt_en: Fix null pointer dereference in bnxt_bs_trace_check_wrap()

In the Linux kernel, the following vulnerability has been resolved: bnxt_en: Fix null pointer dereference in bnxt_bs_trace_check_wrap() With older FW, we may get the ASYNC_EVENT_CMPL_EVENT_ID_DBG_BUF_PRODUCER for FW trace data type that has not been initialized. This will result in a crash in bnxt_bs_trace_type_wrap(). Add a guard to check for a valid magic_byte pointer before proceeding.