file:Fixed incorrect calculation of offset/length
file:Fixed incorrect calculation of offset/length

For reads and writes, the functions currently incorrectly
calculate the offsets/lengths which lead to r/w going out
of range so they fail.

These were the errors from running bonnie++ perf test:

Buffer I/O error on device sda1, logical block 3907228
Buffer I/O error on device sda1, logical block 3907229
blk_update_request: I/O error, dev sda, sector 31573472

Signed-off-by: Bryant G. Ly <1024ba5f11bcf6a7ffb2ce4b8b54f508dfeeefbd@linux.vnet.ibm.com>

JefferyHu/tcmu-runner,superlibj/tcmu-runner,liuy/tcmu-runner,agrover/tcmu-runner,open-iscsi/tcmu-runner,lxbsz/tcmu-runner,open-iscsi/tcmu-runner