staging: r8188eu: remove the pframe variable

staging: r8188eu: remove the pframe variable

Remove the pframe variable, it is no longer used for populating fields of
the outgoing frame.

pmgntframe->buf_addr is already a u8 *, we can drop the (u8 *) cast.

Increment the u8 *pmgntframe->buf_addr by TXDESC_OFFSET before we cast
it to struct ieee80211_mgmt *.

Tested-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220602193726.280922-11-martin@kaiser.cx
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>