pdl: correctly apply mask in ‘write_to’ as well

Before we only applied a mask in ‘parse’, and we always used a
hard-coded mask of the wrong size.

Test: atest pdl_inline_tests
(cherry picked from https://android-review.googlesource.com/q/commit:68efe3a96fb1bee42a6e6318b32b5e840ff0a5eb)
Merged-In: Id499e009d2d83e9eb5e4aaffc375e527a1995864
Change-Id: Id499e009d2d83e9eb5e4aaffc375e527a1995864