Documentation/CodingStyle: allow multiple return statements per function

A surprising number of newbies interpret this section to mean that only
one return statement is allowed per function.  Part of the problem is that
the "one return statement per function" rule is an actual style guideline
that people are used to from other projects.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Eduardo Valentin <eduardo.valentin@ti.com>
Cc: Rob Landley <rob@landley.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>