[util] splice_nexysvideo.sh fix the target directory
[util] splice_nexysvideo.sh fix the target directory

This change fixes an issue introduced in 6379357. When running, script
cannot find required target files due to not specifying the full path
to these files.

Signed-off-by: Silvestrs Timofejevs <5a6466a3751cccdb6ee413d1e87698ed8baaba81@lowrisc.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan