bnxt_en: Fix firmware message delay loop regression.

A recent change to reduce delay granularity waiting for firmware
reponse has caused a regression.  With a tighter delay loop,
the driver may see the beginning part of the response faster.
The original 5 usec delay to wait for the rest of the message
is not long enough and some messages are detected as invalid.

Increase the maximum wait time from 5 usec to 20 usec.  Also, fix
the debug message that shows the total delay time for the response
when the message times out.  With the new logic, the delay time
is not fixed per iteration of the loop, so we define a macro to
show the total delay time.

Fixes: 9751e8e7 ("bnxt_en: reduce timeout on initial HWRM calls")
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>