bnxt_en: Avoid disabling pci device in bnxt_remove_one() for already disabled device.

With the recently added error recovery logic, the device may already
be disabled if the firmware recovery is unsuccessful.  In
bnxt_remove_one(), check that the device is still enabled first
before calling pci_disable_device().

Fixes: 3bc7d4a3 ("bnxt_en: Add BNXT_STATE_IN_FW_RESET state.")
Signed-off-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>