ena: fix build with icc

ena: fix build with icc

With (ICC) 16.0.2 20160204, getting following warnings:

.../drivers/net/ena/base/ena_com.c(492): error #3656: variable
 "flags" may be used before its value is set
 ENA_SPINLOCK_LOCK(admin_queue->q_lock, flags);

.../drivers/net/ena/base/ena_com.c(1971): error #3656: variable
 "mem_handle" may be used before its value is set
 ENA_MEM_ALLOC_COHERENT(ena_dev->dmadev, len,

For both warnings the variable value is ignored, so there is no defect.
To comfort compiler warning, a initial value provided to variables.

Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>