wifi: rtlwifi: Convert LNKCTL change to PCIe cap RMW accessors

The rtlwifi driver comes with custom code to write into PCIe Link
Control register. RMW access for the Link Control register requires
locking that is already provided by the standard PCIe capability
accessors.

Convert the custom RMW code writing into LNKCTL register to standard
RMW capability accessors. The accesses are changed to cover the full
LNKCTL register instead of touching just a single byte of the register.

Fixes: 0c817338

 ("rtl8192ce: Add new driver")
Cc: stable@vger.kernel.org
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20231124084725.12738-3-ilpo.jarvinen@linux.intel.com