Fix partition resize algorithm.

Bug in Fedora documentation on partx, need 1251954, not 1953.  See below.

> partx -g --nr :-1 /dev/mmcblk0
 1    1953 1001953 1000001 488.3M      000ab765-01
 2 1001954 1251953  250000 122.1M      000ab765-02
 3 1251954 3986328 2734375   1.3G      000ab765-03

> partx -g --nr -1:-1 /dev/mmcblk0
 3 1251954 3986328 2734375 1.3G      000ab765-03