base-files: fix sysupgrade 'wget' handling

with r48379 and r48386 the path of wget changed.
respect that and adjust the dirname.

this fixes #21680

Signed-off-by: Bastian Bittorf <bittorf@bluebottle.com>

SVN-Revision: 48451

package/base-files/files/lib/upgrade/common.sh

@@ -48,7 +48,7 @@ supivot() { # <new_root> <old_root>
 
 run_ramfs() { # <command> [...]
 	install_bin /bin/busybox /bin/ash /bin/sh /bin/mount /bin/umount	\
-		/sbin/pivot_root /usr/bin/wget /sbin/reboot /bin/sync /bin/dd	\
+		/sbin/pivot_root /bin/wget /sbin/reboot /bin/sync /bin/dd	\
 		/bin/grep /bin/cp /bin/mv /bin/tar /usr/bin/md5sum "/usr/bin/["	\
 		/bin/dd /bin/vi /bin/ls /bin/cat /usr/bin/awk /usr/bin/hexdump	\
 		/bin/sleep /bin/zcat /usr/bin/bzcat /usr/bin/printf /usr/bin/wc \