ixgbe: initialize data field in struct buffer

While sending request using ixgbe_hic_unlocked() the data field in
buffer struct is not used. It is set when the struct is overwritten by
FW to deliver the response. To not pass random data to FW the whole
structure should be zeroed before use.

Signed-off-by: Krzysztof Galazka <krzysztof.galazka@intel.com>
Signed-off-by: Piotr Pietruszewski <piotr.pietruszewski@intel.com>
Signed-off-by: Guinan Sun <guinanx.sun@intel.com>
Reviewed-by: Wei Zhao <wei.zhao1@intel.com>

Approved by: imp
Obtained from: DPDK (40543be5376ca415b2a7e196315d0555725b8bdf)
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D31621