scan.mk: do not silence output of dump phase

Make it easier to spot currently hidden issues:

 $ make defconfig V=sc
 ...
 Collecting target info: target/linux/airohabash: -c: line 1: syntax error near unexpected token `|'
 bash: -c: line 1: `echo 1686815253<LINUX_VERMAGIC> | staging_dir/host/bin/mkhash md5 | cut -b1-8'
 bash: -c: line 1: syntax error near unexpected token `|'
 bash: -c: line 1: `echo 1686815253<LINUX_VERMAGIC> | staging_dir/host/bin/mkhash md5 | sed -E 's/(.{8})(.{4})(.{4})(.{4})(.{10})../\1-\2-\3-\4-\500/''
 ...

Signed-off-by: Petr Štetiar <ynezz@true.cz>
(cherry picked from commit b522da5b16c7e5952d364b933b921786198f9fe5)