wil6210: move vring_idle_trsh definition to wil6210_priv

vring_idle_trsh is used in the operational driver, hence
should not be defined as a debugfs variable.

Change-Id: I302fbcb7bbf0237ed989828e83c447a8b5c78996
Signed-off-by: Gidon Studinski <qca_gidons@qca.qualcomm.com>
Signed-off-by: Maya Erez <qca_merez@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>
Git-commit: 38d16ab2b2132beeb9777de1508ce2150b2dcd35
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git


Signed-off-by: Maya Erez <merez@codeaurora.org>