src/meta-openembedded:wireshark: fix typo in PACKAGECONFIG[zstd]

ENABLE_STTD is a typo, correct option is ENABLE_ZSTD.

This patches the following CMake warning in do_configure:
  Manually-specified variables were not used by the project: ENABLE_STTD
After, do_configure does not show the warning.

Github issue: openembedded/meta-openembedded#845

Reported-by: Ludovic Jozeau <ludovic.jozeausmile.fr>
Reviewed-by: Yoann Congal <yoann.congalsmile.fr>
Signed-off-by: Ghislain Mangé <ghislain.mangesmile.fr>
Signed-off-by: Khem Raj <raj.khemgmail.com>