handle errors on exits from subshells

most of these are probably redundant, and will never
be called, but lbmk needs to be as safe as possible
under fault conditions. fail early, fail hard.

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

include/git.sh

@@ -72,7 +72,7 @@ prepare_new_tree()
 		git submodule update --init --checkout || \
 		    err "prepare_new_tree ${project}/${tree}: !submodules"
 	fi
-	)
+	) || err "git submodule update failure"
 	git_am_patches "${tmp_git_dir}" "$PWD/$cfgsdir/$tree/patches" || \
 	    err "prepare_new_tree ${project}/${tree}: patch fail"
 	[ "${patchfail}" = "y" ] && err "PATCH FAIL"
@@ -138,7 +138,7 @@ git_reset_rev()
 		git submodule update --init --checkout || \
 		    err "git_reset_rev ${1}: can't download submodules"
 	fi
-	)
+	) || err "git reset fail"
 }
 
 git_am_patches()