brcmfmac: decrease the range of SDIO access lock

Semaphore sdsem which protects consecutive SDIO bus access is used
to lock down unnecessary wide range. Decrease the locking range
provides the capability of parallel processing.

Signed-off-by: Franky Lin <frankyl@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>