bnxt_en: Fix zero padding of tx push data.

The arithmetic to zero pad the last 64-bit word in the push buffer is not
correct.

1. It should be pdata + length to get to the end.
2. 'pdata' is void pointer and passing it to PTR_ALIGN() will cast the
aligned pointer to void.  Pass 'end' which is u64 pointer to PTR_ALIGN()
instead so that the aligned pointer - 1 is the last 64-bit pointer to data.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>