staging: rts5208: Use array_size() helper in vmalloc() and memset()

The vmalloc() function has no 2-factor argument form, so multiplication
factors need to be wrapped in array_size(). Also, while there, use
array_size() in memset().

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/20200616175543.GA28687@embeddedor


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