For one, it that way matches reality (as it returns sal_uInt16, not short or
sal_Int16) and its SVBT32ToUInt32 counterpart.  For another, I plan a follow-up
commit of introducing an additional SVBT16ToInt16 to explicitly return
sal_Int16.

Change-Id: I28915e6593ccdca0c11d7b2fa593e96e359a9532
Reviewed-on: https://gerrit.libreoffice.org/68686
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>