net/cxgbe/base: initialize variable before reading EEPROM

net/cxgbe/base: initialize variable before reading EEPROM

data value could have been garbage if VPD access timed out for VPD read
request could not been issued.

Found with clang static analysis:
drivers/net/cxgbe/base/t4_hw.c:1577:22:
warning: The left operand of '&' is a garbage value
        } while ((stats_reg & 0x1) && --max_poll);
                  ~~~~~~~~~ ^

Fixes: fe0bd9ee5da3 ("net/cxgbe: support EEPROM access")
Cc: stable@dpdk.org
Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>