fate/pixfmts: use the appropriate variable names for temporary files.

${1} is now the filter args and is inappropriate as a unique name for
the test (and causes some FATE issues because of the ':' in them).
${filter} is not used either to replace the ${1} because ${outfile}
already contains a unique name for the test.

tests/fate-run.sh

@@ -185,10 +185,10 @@ pixfmts(){
     prefilter_chain=$2
 
     showfiltfmts="$target_exec $target_path/libavfilter/filtfmts-test"
-    scale_exclude_fmts=${outfile}${1}_scale_exclude_fmts
-    scale_in_fmts=${outfile}${1}_scale_in_fmts
-    scale_out_fmts=${outfile}${1}_scale_out_fmts
-    in_fmts=${outfile}${1}_in_fmts
+    scale_exclude_fmts=${outfile}_scale_exclude_fmts
+    scale_in_fmts=${outfile}_scale_in_fmts
+    scale_out_fmts=${outfile}_scale_out_fmts
+    in_fmts=${outfile}_in_fmts
 
     # exclude pixel formats which are not supported as input
     $showfiltfmts scale | awk -F '[ \r]' '/^INPUT/{ fmt=substr($3, 5); print fmt }' | sort >$scale_in_fmts