bnxt_en: Fix null pointer dereference in bnxt_bs_trace_check_wrap()

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.

Fixes: 84fcd9449fd7 ("bnxt_en: Manage the FW trace context memory")
Reviewed-by: Somnath Kotur <somnath.kotur@broadcom.com>
Reviewed-by: Shruti Parab <shruti.parab@broadcom.com>
Signed-off-by: Gautam R A <gautam-r.a@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Link: https://patch.msgid.link/20251104005700.542174-4-michael.chan@broadcom.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>