checkpatch: optimise statement scanner when mid-statement

In the middle of a long definition or similar, there is no possibility of
finding a smaller sub-statement.  Optimise this case by skipping statement
aquirey where there are no starts of statement (open brace '{' or
semi-colon ';').  We are likely to scan slightly more than needed still
but this is safest.

Signed-off-by: Andy Whitcroft <apw@canonical.com>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>