eal: fix auxv open check for ARM and PPC

eal: fix auxv open check for ARM and PPC

The assertion of return value from the open() function is done against
0, while it is a correct value - open() returns -1 in case of an error.
It causes problems while trying to run as a daemon, in which case, this
call to open() will return 0 as a valid descriptor.

Fixes: b94e5c9406b5 ("eal/arm: add CPU flags for ARMv7")
Fixes: 97523f822ba9 ("eal/arm: add CPU flags for ARMv8")
Fixes: 9ae155385686 ("eal/ppc: cpu flag checks for IBM Power")
Cc: stable@dpdk.org
Signed-off-by: Lukasz Majczak <lma@semihalf.com>
Acked-by: Jan Viktorin <viktorin@rehivetech.com>
Acked-by: Chao Zhu <chaozhu@linux.vnet.ibm.com>