Fixed incorrect Flash size for UM FeatherS3 Neo build flash size (#10614)

Signed-off-by: Seon Rozenblum <[email protected]>

Author: UnexpectedMaker

Diff for: boards.txt

@@ -3895,7 +3895,7 @@ um_feathers3neo.build.cdc_on_boot=1
 um_feathers3neo.build.msc_on_boot=0
 um_feathers3neo.build.dfu_on_boot=0
 um_feathers3neo.build.f_cpu=240000000L
-um_feathers3neo.build.flash_size=16MB
+um_feathers3neo.build.flash_size=8MB
 um_feathers3neo.build.flash_freq=80m
 um_feathers3neo.build.flash_mode=dio
 um_feathers3neo.build.boot=qio