Makefile: fix extra parenthesis typo when CC_STACKPROTECTOR_REGULAR is enabled

An extra parenthesis typo introduced in 19952a92 ("stackprotector:
Unify the HAVE_CC_STACKPROTECTOR logic between architectures") is
causing the following error when CONFIG_CC_STACKPROTECTOR_REGULAR is
enabled:

  Makefile:608: Cannot use CONFIG_CC_STACKPROTECTOR: -fstack-protector not supported by compiler
  Makefile:608: *** missing separator.  Stop.

Signed-off-by: Fathi Boudra <fathi.boudra@linaro.org>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>