staging: r8188eu: use ieee80211 helper for protected bit

Use ieee80211_has_protected to check if the "protected" bit is set. Remove
the r8188eu driver's internal macro for this check.

Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20221126154253.178275-6-martin@kaiser.cx


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>