e2fsck: fix kernel compat functions to use kernel error return conventions

e2fsck: fix kernel compat functions to use kernel error return conventions

Fix journal_bmap() and sync_blockdev() to use the kernel error
convetions (e.g., -EIO instead of EIO) since they are called by
reovery.c, which is shared userspace / kernel code.

Without this, e2fsck might print an error message like this:

/sbin/e2fsck: Unknown code ____ 251 while recovering journal of /dev/mapper/thin-vol

instead of what it should have printed which was this:

/sbin/e2fsck: Input/output error while recovering journal of /dev/mapper/thin-vol

Signed-off-by: Theodore Ts'o <tytso@mit.edu>