net/bnxt: add null check for resource manager
net/bnxt: add null check for resource manager

Verify the resource manager has been allocated prior to using it.
This can avoid potential segmentation faults.

Signed-off-by: Shahaji Bhosle <d4241bc51bf8c875050899ee5aba48754e474d6f@broadcom.com>
Reviewed-by: Mike Baucom <c089d82d6780f221b7ddfeedb35afd8fb349c608@broadcom.com>
Reviewed-by: Ajit Khaparde <01965fbd61169dc18f3fb5e13de7f67d298f8924@broadcom.com>

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