wil6210: drop -Werror compiler flag

In production code, don't use -Werror,
as it causes random compilation failures due to compiler version and options used.

With every new version of gcc, it becomes stricter and report more warnings.

Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>