Staging: rts5208: Introduce a new variable to shorten line length and increase readability

The variable block_no is introduced so as to shorten line length
in the long assignment statement and increase readability.

Signed-off-by: Vatika Harlalka <vatikaharlalka@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>