net/bnxt: fix lock release on NVM write failure

net/bnxt: fix lock release on NVM write failure

In bnxt_hwrm_flash_nvram, before attempting to allocate a buffer
we are grabbing the rte_spinlock. And if the allocation fails we
are returning before releasing the spinlock. We avoid the situation
by calling HWRM_PREP which grabs the lock after the buffer is
allocated successfully.

Fixes: 19e6af01bb36 ("net/bnxt: support get/set EEPROM")
Cc: stable@dpdk.org
Signed-off-by: Ajit Khaparde <ajit.khaparde@broadcom.com>
Reviewed-by: Randy Schacher <stuart.schacher@broadcom.com>