JFS: use DIV_ROUND_UP where appropriate

This replaces some macros and code, which do the same thing as DIV_ROUND_UP
defined in kernel.h, to use the DIV_ROUND_UP macro.

Signed-off-by: Shaun Zinck <shaun.zinck@gmail.com>
Signed-off-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>