Documentation: blackfin: Makefile: Typo building issue

Miss a ')' for ifneq in Makefile, the related building error:

  Documentation/blackfin/Makefile:2: *** invalid syntax in conditional.  Stop.
  make[1]: *** [Documentation/blackfin] Error 2
Signed-off-by: NChen Gang <gang.chen.5i5j@gmail.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/blackfin/Makefile

 ifneq ($(CONFIG_BLACKFIN),)
-ifneq ($(CONFIG_BFIN_GPTIMERS,)
+ifneq ($(CONFIG_BFIN_GPTIMERS),)
 obj-m := gptimers-example.o
 endif
 endif