vcomp/jpegxs: reduce default BPP=7/10

the value 3 seems to be very large as a default value

If the user omits the setting, it easily exceeeds 1 Gbps for
2160p60. Equivalent for JPEG Q=75 might be something like 0.5-0.7 so
using the upper bound.

src/video_compress/jpegxs.cpp

@@ -129,7 +129,8 @@ state_video_compress_jpegxs::state_video_compress_jpegxs(struct module *parent,
                 throw 1;
         }
 
-        encoder.bpp_numerator = 3;
+        encoder.bpp_numerator = 7;
+        encoder.bpp_denominator = 10;
         encoder.verbose = VERBOSE_NONE;
         encoder.threads_num = get_cpu_core_count();