[bio][flash][stm32f7xx] Write block returns number of bytes written
[bio][flash][stm32f7xx] Write block returns number of bytes written

Test Plan: Tested

Differential Revision: http://phab.gkalsi.com/D3

minglun-tsai/lk,ErikCorryGoogle/lk,ErikCorryGoogle/lk,minglun-tsai/lk,littlekernel/lk,sndnvaps/lk,sndnvaps/lk,hollanderic/lkstuff,hollanderic/lkstuff,sndnvaps/lk,minglun-tsai/lk,travisg/lk,travisg/lk,hollanderic/lkstuff,ErikCorryGoogle/lk,travisg/lk,littlekernel/lk,littlekernel/lk,littlekernel/lk,hollanderic/lkstuff,sndnvaps/lk,travisg/lk,minglun-tsai/lk,sndnvaps/lk,ErikCorryGoogle/lk