MdeModulePkg:Fix the issue that refresh the question fail in DriverSample

MdeModulePkg:Fix the issue that refresh the question fail in DriverSample

Once the question is refreshed,the processing should happen in the callback function
of EFI_BROWSER_ACTION_RETRIEVE case,rather than EFI_BROWSER_ACTION_CHANGING in DriverSample.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18150 6f19259b-4bc3-4df7-8a09-765794883524