[POWERPC] PS3: Fix bug where the major version part is not compared

Fix the bug that the major version part of the firmware version number
is ignored in the comparison done by ps3_compare_firmware_version
because the difference of two 64-bit quantities is returned as an int.

Signed-off-by: Masakazu Mokuno <mokuno@sm.sony.co.jp>
Acked-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>