ion: Fix sparse non static symbol warnings

Fixes the following sparse warnings:

drivers/staging/android/ion/ion_dummy_driver.c:26:19: warning: symbol 'idev' was not declared. Should it be static?
drivers/staging/android/ion/ion_dummy_driver.c:27:17: warning: symbol 'heaps' was not declared. Should it be static?
drivers/staging/android/ion/ion_dummy_driver.c:29:6: warning: symbol 'carveout_ptr' was not declared. Should it be static?
drivers/staging/android/ion/ion_dummy_driver.c:30:6: warning: symbol 'chunk_ptr' was not declared. Should it be static?
drivers/staging/android/ion/ion_dummy_driver.c:32:26: warning: symbol 'dummy_heaps' was not declared. Should it be static?
drivers/staging/android/ion/ion_dummy_driver.c:59:26: warning: symbol 'dummy_ion_pdata' was not declared. Should it be static?

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>