bnxt_en: Fix NULL pointer crash in bnxt_ptp_enable during error cleanup

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

bnxt_en: Fix NULL pointer crash in bnxt_ptp_enable during error cleanup

When bnxt_init_one() fails during initialization (e.g.,
bnxt_init_int_mode returns -ENODEV), the error path calls
bnxt_free_hwrm_resources() which destroys the DMA pool and sets
bp->hwrm_dma_pool to NULL. Subsequently, bnxt_ptp_clear() is called,
which invokes ptp_clock_unregister().

Since commit a60fc3294a37 ("ptp: rework ptp_clock_unregister() to
disable events"), ptp_clock_unregister() now calls
ptp_disable_all_events(), which in turn invokes the driver's .enable()
callback (bnxt_ptp_enable()) to disable PTP events before completing the
unregistration.

bnxt_ptp_enable() attempts to send HWRM commands via bnxt_ptp_cfg_pin()
and bnxt_ptp_cfg_event(), both of which call hwrm_req_init(). This
function tries to allocate from bp->hwrm_dma_pool, causing a NULL
pointer dereference:

bnxt_en 0000:01:00.0 (unnamed net_device) (uninitialized): bnxt_init_int_mode err: ffffffed
KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
Call Trace:
__hwrm_req_init (drivers/net/ethernet/broadcom/bnxt/bnxt_hwrm.c:72)
bnxt_ptp_enable (drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c:323 drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c:517)
ptp_disable_all_events (drivers/ptp/ptp_chardev.c:66)
ptp_clock_unregister (drivers/ptp/ptp_clock.c:518)
bnxt_ptp_clear (drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c:1134)
bnxt_init_one (drivers/net/ethernet/broadcom/bnxt/bnxt.c:16889)

Lines are against commit f8f9c1f4d0c7 ("Linux 6.19-rc3")

Fix this by clearing and unregistering ptp (bnxt_ptp_clear()) before
freeing HWRM resources.