surfaceflinger: Fix range check for getFormat

Fix potential buffer overflow error in getFormat with indices
greater than MAX_HWC_DISPLAYS.

Change-Id: I5e5b69d8d043e900f5e33ca9a62e94ae5f857b68
(cherry picked from commit 4e3e30c2d5a2a6f7dc4ee8696b1ac2a52dffd5dc)
1 file changed