fs: clean up around fs_type

fs_ls(), fs_mkdir() and fs_unlink() sets fs_type to FS_TYPE_ANY
explicitly, but it is redundant as they call fs_close().
So just remove those lines.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>