wil6210: fix warning in pointer arithmetic

In some compilation environments, result of pointer arithmetic interpreted as int
while in others it is long int. Force conversion to long.

Change-Id: Idc2e88090b5d6b42261eda6f977d2061529aba0a
Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Git-commit: 7cd4ec55178973822de45ff8f135d62df66c7961
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/linville/wireless-testing.git


Signed-off-by: Hamad Kadmany <hkadmany@codeaurora.org>