brcmfmac: Remove bandaid for SleepCSR

Register access code is not the place for band-aid fixes like this.
If this is a genuine problem, it should be fixed further up in the driver
stack.

Signed-off-by: Ian Molton <ian@mnementh.co.uk>
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>