enic: fix uninitialized variable

enic: fix uninitialized variable

The variable notify_pa is only initialized inside one branch of
an if statement, triggering a compiler error with clang 3.3 on FreeBSD.

  CC vnic/vnic_dev.o
lib/librte_pmd_enic/vnic/vnic_dev.c:777:6: fatal error: variable 'notify_pa'
      is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
        if (!vnic_dev_in_reset(vdev)) {

Fix this issue by adding "= 0" to the variable definition.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>