bnxt_en: Improve TQM ring context memory sizing formulas.

The current formulas to calculate the TQM slow path and fast path ring
context memory sizes are not quite correct.  TQM slow path entry is
array index 0 of ctx->tqm_mem[].  The other array entries are for fast
path.  Fix these sizes according to latest firmware spec. for 57500 and
newer chips.

Fixes: 3be8136c ("bnxt_en: Initialize context memory to the value specified by firmware.")
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>