brcmfmac: remove redundant retries for SDIO core register access

The new brcmf_sdio_regrl/regwl interface has already performed
retries on failed attempts. It is no longer necessary to have the
retry mechanism in r_sdreg32/w_sdreg32.

Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Franky Lin <frankyl@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>