wilc1000: changes for SPI communication stall issue found with Iperf

Added retry mechanism to ensure VMM enable bit is set during the
block transfer of data between host and WILC FW.

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201208103739.28597-1-ajay.kathat@microchip.com