rsi: rename sdio_read_buffer_status_register

rsi_sdio_check_buffer_status would be the appropriate name
for this function as we are checking hardware buffers
availability status.

Signed-off-by: Karun Eagalapati <karun256@gmail.com>
Signed-off-by: Amitkumar Karwar <amit.karwar@redpinesignals.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>