staging: rts5208: Assign array_size() to a variable

Assign array_size() to variable _size_ and use it in multiple places.

This issue was found with the help of Coccinelle and, audited and fixed
manually.

Addresses-KSPP-ID: https://github.com/KSPP/linux/issues/83


Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20200710183350.GA8376@embeddedor


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>