multimedia/svt-av1: unbreak WITH_DEBUG= build

FAILED: Source/Lib/ASM_SSE2/CMakeFiles/ASM_SSE2.dir/EbPictureOperators_SSE2.asm.o
/usr/local/bin/nasm -ISource/API -ISource/Lib/Codec -ISource/Lib/C_DEFAULT -ISource/Lib/ASM_SSE2 -DUNIX64 -g null -f elf64 -o Source/Lib/ASM_SSE2/CMakeFiles/ASM_SSE2.dir/EbPictureOperators_SSE2.asm.o Source/Lib/ASM_SSE2/EbPictureOperators_SSE2.asm
null: fatal: more than one input file specified: Source/Lib/ASM_SSE2/EbPictureOperators_SSE2.asm