get.sh: use git-show instead, for rev checks

whatchanged is deprecated, and results in an error
on modern git versions, prompting you to include
the --i-still-use-this argument

what absolute, utter fucking arrogance. i use the
whatchanged feature every fucking day.

i will be complaining to git-scm.com about this.

but that's what we do in libreboot. we adapt.

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/get.sh

@@ -288,7 +288,7 @@ try_git()
 		x_ mv "$tmpgitcache" "$gitdest"
 	fi
 
-	if git -C "$gitdest" whatchanged "$7" 1>/dev/null 2>/dev/null && \
+	if git -C "$gitdest" show "$7" 1>/dev/null 2>/dev/null && \
 	    [ "$forcepull" != "y" ]; then
 		# don't try to pull the latest changes if the given target
 		# revision already exists locally. this saves a lot of time