wil6210: use writel_relaxed in wil_debugfs_iomem_x32_set

writel_relaxed can be used in wil_debugfs_iomem_x32_set
since there is a wmb call immediately after.

Signed-off-by: Lior David <liord@codeaurora.org>
Signed-off-by: Maya Erez <merez@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>