nanobsd: embedded: Fix more regressions from last cleanup

Commit c99bb5747f changed "()" grouping into "{}", but in these cases
we chdir and depended on the subshell not changing the directory for the
caller.  Restore the old behavior.  While things appear to work without
this change, the previous code was intentionally structured this way.

Reviewed by:	imp
Fixes:		c99bb5747f ("nanobsd: minor formatting cleanup")
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D54978

tools/tools/nanobsd/embedded/common

@@ -116,11 +116,11 @@ add_etc_make_conf() {
 }
 customize_cmd add_etc_make_conf
 
-cust_install_machine_files() {
+cust_install_machine_files() (
 	echo "cd ${NANO_CFG_BASE}/Files"
 	cd ${NANO_CFG_BASE}/Files
 	find . -print | grep -Ev '/(CVS|\.svn|\.hg|\.git)' | cpio -dumpv ${NANO_WORLDDIR}
-}
+)
 customize_cmd cust_install_files
 customize_cmd cust_install_machine_files
 
@@ -431,7 +431,7 @@ typical_embedded() {
 }
 customize_cmd typical_embedded
 
-fix_pkg() {
+fix_pkg() (
 	chdir ${NANO_WORLDDIR}
 	mkdir -p pkg
 	mkdir -p pkg/db
@@ -450,7 +450,7 @@ fix_pkg() {
 	echo "./pkg/db type=dir uname=root gname=wheel mode=0755"
 	echo "./pkg/tmp type=dir uname=root gname=wheel mode=0755"
 	) >> ${NANO_METALOG}
-}
+)
 customize_cmd fix_pkg
 
 save_build() {
@@ -476,7 +476,7 @@ customize_cmd shrink_md_fbsize
 
 customize_cmd cust_comconsole
 
-dos_boot_part() {
+dos_boot_part() (
 	local d=/usr/local/share/u-boot/${NANO_BOOT_PKG}
 	local f=${NANO_FAT_DIR}
 
@@ -493,7 +493,7 @@ dos_boot_part() {
 
 	# Now we need to copy over dtb files from the build.
 	cp ${NANO_WORLDDIR}/boot/dtb/*.dtb .
-}
+)
 
 if [ -n "$NANO_BOOT_PKG" ]; then
 	d=/usr/local/share/u-boot/${NANO_BOOT_PKG}