Fix redoxfs fmap using incorrect offset

3 jobs for master in 1 minute and 14 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #11481
build:linux:cargo

00:01:14

failed #11482
build:redox:cargo

00:01:07

 
  Test
skipped #11483
test:linux:cargo
 
Name Stage Failure
failed
build:redox:cargo Build
error: Could not compile `redoxfs`.

Caused by:
process didn't exit successfully: `rustc --crate-name redoxfs src/bin/mount.rs --color never --crate-type bin --emit=dep-info,link -C debuginfo=2 -C metadata=0fd87e631f79608a -C extra-filename=-0fd87e631f79608a --out-dir /builds/redox-os/redoxfs/target/x86_64-unknown-redox/debug/deps --target x86_64-unknown-redox -C linker=x86_64-unknown-redox-gcc -C incremental=/builds/redox-os/redoxfs/target/x86_64-unknown-redox/debug/incremental -L dependency=/builds/redox-os/redoxfs/target/x86_64-unknown-redox/debug/deps -L dependency=/builds/redox-os/redoxfs/target/debug/deps --extern syscall=/builds/redox-os/redoxfs/target/x86_64-unknown-redox/debug/deps/libsyscall-ec7e7d4c12a86885.rlib --extern redoxfs=/builds/redox-os/redoxfs/target/x86_64-unknown-redox/debug/deps/libredoxfs-a1eeebf47c68447a.rlib --extern spin=/builds/redox-os/redoxfs/target/x86_64-unknown-redox/debug/deps/libspin-12c609d445dd7203.rlib --extern uuid=/builds/redox-os/redoxfs/target/x86_64-unknown-redox/debug/deps/libuuid-17a7d8bac6b3e387.rlib` (exit code: 1)
warning: build failed, waiting for other jobs to finish...
error: build failed
groupadd: group 'redox' already exists
useradd: user 'redox' already exists
ERROR: Job failed: exit code 1