bnxt_en: Fix possible corrupted NVRAM parameters from firmware response.

In bnxt_find_nvram_item(), it is copying firmware response data after
releasing the mutex.  This can cause the firmware response data
to be corrupted if the next firmware response overwrites the response
buffer.  The rare problem shows up when running ethtool -i repeatedly.

Fix it by calling the new variant _hwrm_send_message_silent() that requires
the caller to take the mutex and to release it after the response data has
been copied.

Fixes: 3ebf6f0a

 ("bnxt_en: Add installed-package version reporting via Ethtool GDRVINFO")
Reported-by: Sarveswara Rao Mygapula <sarveswararao.mygapula@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>