brcmfmac: Minimize SDIO dpc scheduling.

SDIO dpc scheduling is done (repeated) when counter is set. This
counter gets decreased when dpc is finished. It is more efficient
to set counter to 0 before the dpc is actullay run. This will
minimize the frequency with which dpc is executed.

Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Daniel (Deognyoun) Kim <dekim@broadcom.com>
Signed-off-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>