brcmfmac: stop releasing sdio host in irq handler

brcmf_sdbrcm_isr doesn't access to the dongle through SDIO bus.
Stop releasing and claiming host in irq handler to eliminate
any potential risk.

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>