checkpatch: improve 'bare use of' signed/unsigned types warning

Fix false positive warning of identifiers ending in signed with an =
assignment of WARNING: Prefer 'signed int' to bare use of 'signed'.

Link: http://lkml.kernel.org/r/6a0e24c3e9102337528ecfcbbe91a0eb5b4820ed.1469529497.git.joe@perches.com


Signed-off-by: Joe Perches <joe@perches.com>
Reported-by: Alan Douglas <alanjhd@gmail.com>
Acked-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>