[minor] build_dpdk.sh - git am command path fix

[MateuszGrabuszynski]

The git am command does use a path which drills down too little (does not hit the patches folder) and fails the script entirely.

[skolelis]

lgtm

[MateuszGrabuszynski]

One remark from @skolelis was raised - this is dependent on the directory from which the script is executed. My intention is to always execute from the same exact directory (./build-dpdk ...), and I have not found the script used/sourced anywhere else.