Fix STM AlternateByteSize calculation

05899e9 introduces a shift of
by QUADSPI_CCR_ABSIZE_POS for AddressSize and AlternateBytesSize.
But for AlternateBytesSize the old code that set it directly from
command->alt.size was left in place, causing the new shifted value
to be ignored.

Author: Matthew Macovsky

targets/TARGET_STM/qspi_api.c

@@ -252,7 +252,6 @@ void qspi_prepare_command(const qspi_command_t *command, QSPI_CommandTypeDef *st
         st_command->AlternateBytes = command->alt.value;
         /* command->AlternateBytesSize needs to be shifted by QUADSPI_CCR_ABSIZE_Pos */
         st_command->AlternateBytesSize = (command->alt.size << QUADSPI_CCR_ABSIZE_Pos) & QUADSPI_CCR_ABSIZE_Msk;
-        st_command->AlternateBytesSize = command->alt.size;
     }
 
     switch (command->data.bus_width) {