checkpatch: fix function pointers in blank line needed after declarations test

Add a function pointer declaration check to the test for blank line
needed after declarations.

Signed-off-by: Joe Perches <joe@perches.com>
Reported-by: Bruce W Allan <bruce.w.allan@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>