hack/init-buildx.sh: fix broken patter matching

Author: marquiz

hack/init-buildx.sh

@@ -21,7 +21,7 @@ export DOCKER_CLI_EXPERIMENTAL=enabled
 # AND if it isn't the docker driver, which doesn't work
 current_builder="$(docker buildx inspect)"
 # linux/amd64, linux/arm64, linux/riscv64, linux/ppc64le, linux/s390x, linux/386, linux/arm/v7, linux/arm/v6
-if ! grep -q "^Driver: docker$"  <<<"${current_builder}" && \
+if ! grep -Eq "^Driver:\s*docker$"  <<<"${current_builder}" && \
      grep -q "linux/amd64" <<<"${current_builder}" && \
      grep -q "linux/arm64" <<<"${current_builder}"; then
   exit 0