staging: rtl8723bs: remove unused 'poll_cnt' from rtw_set_rpwm()

staging: rtl8723bs: remove unused 'poll_cnt' from rtw_set_rpwm()

The 'poll_cnt' is used to assist in polling hardware state. Current code
uses jiffies to determine timeout, so removing this value is safe.

Otherwise, clang warns:

core/rtw_pwrctrl.c:288:6: warning:
	 variable 'poll_cnt' set but not used [-Wunused-but-set-variable]
  288 |                 u8 poll_cnt = 0;
      |                    ^

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com>
Link: https://lore.kernel.org/r/20240913002815.5149-5-pkshih@realtek.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>