wifi: nrf_wifi: add alignment requirement to buffers

The nRF lower levels (`spim_addr_check` and `qspi_addr_check`) do
address alignment validation before sending or receiving data. If the
buffer sizes are not aligned, errors like this are printed to the
console when the interface is powered up.

```
<err> : spim_addr_check : Unaligned address ee0b2 2002b020 1 0 0
<err> : spim_addr_check : Unaligned address eeb3e 2002bb40 1 0 0
<err> : spim_addr_check : Unaligned address ef5ca 2002c660 1 0 0
<err> : spim_addr_check : Unaligned address f0056 2002d180 1 0 0
```

Signed-off-by: Jordan Yates <jordan@embeint.com>