staging: r8188eu: remove constant variable eRFPath

In the _PHY_SwChnl8192C function, eRFPath is always zero. Remove the
variable and use 0 in the code. Replace (enum rf_radio_path)0 with
RF_PATH_A.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220204090941.309900-5-martin@kaiser.cx


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