fuse_lseek_backing was returning the offset as an int, which would then
be treated as an ERR if in the range 4G-4096 and 4G.

Although the call would appear to work correctly, the file position
would be incorrect according to a subsequent fseek with SEEK_CUR.

Based on a change by chenyuwen <chenyuwen1@meizu.com> who found and
fixed this issue.

Bug: 319219307
Change-Id: I3aef5fb22751a72ce2bd7674ee081956a89fc752
Signed-off-by: chenyuwen <chenyuwen1@meizu.com>
Signed-off-by: Paul Lawrence <paullawrence@google.com>