checkpatch: fix false errors due to macro concatenation

The macro concatenation (##) sequence can cause false errors when checking
macro's.  Checkpatch doesn't currently know about the operator.

For example this line,

+ 	entry = (struct ftrace_raw_##call *)raw_data;                   \

is correct but it produces the following error,

ERROR: need consistent spacing around '*' (ctx:WxB)
+       entry = (struct ftrace_raw_##call *)raw_data;\
                                          ^

The line above doesn't have any spacing problems, and if you remove the
macro concatenation sequence checkpatch doesn't give any errors.

Extend identifier handling to include ## concatenation within the
definition of an identifier.

Reported-by: Daniel Walker <dwalker@fifo99.com>
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>