staging: rtl8712: Remove unnecessary ret variable

Since the variable ret is set at the beginning of the function and
never changes its value, we can just return the value it was set to.

Found using coccinelle with misc/returnvar.cocci.

Signed-off-by: Joseph Bisch <joseph.bisch@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>