examples: hide error for missing pkg-config path flag

examples: hide error for missing pkg-config path flag

Some versions of pkg-config don't support the --path flag, which is not a
fatal error when building the apps. Without the flag, the makefile just
cannot track the .pc file of DPDK as a dependency of the build. Therefore,
we can ignore the error and suppress it by redirecting to /dev/null the
stderr from that call to pkg-config.

Fixes: 22119c4591a0 ("examples: use pkg-config in makefiles")
Cc: stable@dpdk.org
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Tested-by: Ferruh Yigit <ferruh.yigit@intel.com>