ZFS: Fix compile warning in cmd_zfs.c (GCC 4.6.4 from ELDK 5.2.1)

This patch fixes the following compile warnings:

cmd_zfs.c:177:1: warning: initialization from incompatible pointer type [enabled by default]
cmd_zfs.c:177:1: warning: (near initialization for '_u_boot_list_cmd_zfsls.cmd') [enabled by default]
cmd_zfs.c:182:1: warning: initialization from incompatible pointer type [enabled by default]
cmd_zfs.c:182:1: warning: (near initialization for '_u_boot_list_cmd_zfsload.cmd') [enabled by default]

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Jorgen Lundman <lundman@lundman.net>