staging: rtl8192e: Remove unused variable RF_C_TxPwDiff

RF_C_TxPwDiff is set to a value and then never evaluated. Remove resulting
dead code.

Signed-off-by: Philipp Hortmann <philipp.g.hortmann@gmail.com>
Link: https://lore.kernel.org/r/bcace15cc05057ab310f807f27619ef6ff391d91.1674071236.git.philipp.g.hortmann@gmail.com


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