galaxys2-common: camera: exynos_exif.c: fix values of some wrong EXIF tags

 * adapt the code to the changes made in Exif.h
 * calculate ExposureTime from the ShutterSpeedValue: the exposure time
   read from the camera doesn't seem to work

Together with changes in Exif.h, this commit fixes ExposureTime, FNumber,
ShutterSpeedValue, ApertureValue, BrightnessValue and MaxApertureValue.

The values now match what was generated by the closed camera driver.

Credits to tryptophane for ExposureTime and ShutterSpeedValue. Thanks to
opaco23 and stone_ship who provided samples.

This commit requires http://review.cyanogenmod.org/37370

Change-Id: I16b606e65e895b98f9679ffb6172869c2cbe741c