reiserfs: rework reiserfs_warning

ReiserFS warnings can be somewhat inconsistent.
In some cases:
 * a unique identifier may be associated with it
 * the function name may be included
 * the device may be printed separately

This patch aims to make warnings more consistent. reiserfs_warning() prints
the device name, so printing it a second time is not required. The function
name for a warning is always helpful in debugging, so it is now automatically
inserted into the output. Hans has stated that every warning should have
a unique identifier. Some cases lack them, others really shouldn't have them.
reiserfs_warning() now expects an id associated with each message. In the
rare case where one isn't needed, "" will suffice.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>