rtlwifi: remove return in _rtl_pci_switch_clk_req

the return value from _rtl_pci_switch_clk_req is not used by any of its callers.

Signed-off-by: Devendra.Naga <devendra.aaru@gmail.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>