samples: bpf: Fix a spelling typo in do_hbm_test.sh

This patch fixes a spelling typo in do_hbm_test.sh

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210315124454.1744594-1-standby24x7@gmail.com