[PATCH] v9fs: Change error magic numbers to defined constants

Change magic error numbers to system defined constants in v9fs error.h As
suggested by Jan-Benedict Glaw.

Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>