staging: wilc1000: remove a macro WILC_NULLCHECK

This patch replaces WILC_NULLCHECK with the plain statements and then removes
the macro WILC_NULLCHECK in wilc_errorsupport.h which is not used anymore.

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>