staging: wfx: fix endianness of the field 'num_tx_confs'

staging: wfx: fix endianness of the field 'num_tx_confs'

The field 'num_tx_confs' from the struct hif_cnf_multi_transmit is a
__le32. Sparse complains this field is not always correctly accessed:

    drivers/staging/wfx/hif_rx.c:82:9: warning: restricted __le32 degrades to integer
    drivers/staging/wfx/hif_rx.c:87:29: warning: restricted __le32 degrades to integer

However, the value of num_tx_confs cannot be greater than 15. So, we
only have to access to the least significant byte. It is finally easier
to declare it as an array of bytes and only access to the first one.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200512150414.267198-16-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>