staging: r8188eu: remove HW_VAR_RXDMA_AGG_PG_TH from SetHwReg8188EU()

staging: r8188eu: remove HW_VAR_RXDMA_AGG_PG_TH from SetHwReg8188EU()

The HW_VAR_RXDMA_AGG_PG_TH case in SetHwReg8188EU() just sets a
variable conditionally and then calls rtw_write8(). Set the variable
in the caller and call rtw_write8() directly. Move the functionality
into a new static function to make the code cleaner. Remove the
HW_VAR_RXDMA_AGG_PG_TH case from SetHwReg8188EU(). This is part of the
ongoing effort to get rid of the unwanted hal layer.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20220329202141.7028-6-straube.linux@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>