endian.h: avoid some Wconversion warnings

Change-Id: Ic77bd0dd6ac2355eaf3e11811fba7604c782d9d6
Reviewed-on: https://gerrit.libreoffice.org/17307Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>

include/osl/endian.h

@@ -161,7 +161,7 @@ extern "C" {
 #endif
 
 #ifndef OSL_MAKEWORD
-#   define OSL_MAKEWORD(bl, bh)    ((sal_uInt16)((bl) & 0xFF) | (((sal_uInt16)(bh) & 0xFF) << 8))
+#   define OSL_MAKEWORD(bl, bh)    ((sal_uInt16)((sal_uInt16)((bl) & 0xFF) | (((sal_uInt16)(bh) & 0xFF) << 8)))
 #endif
 #ifndef OSL_LOBYTE
 #   define OSL_LOBYTE(w)           ((sal_uInt8)((sal_uInt16)(w) & 0xFF))