staging: wilc1000: rename the member variable, drvHandler of host_if_msg

This patch renames drvHandler of struct host_if_msg to drv.

Signed-off-by: Leo Kim <leo.kim@atmel.com>
Signed-off-by: Tony Cho <tony.cho@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>