ath9k: Remove set but not used variable

This addresses the following gcc warning with "make W=1":

drivers/net/wireless/ath/ath9k/ar9580_1p0_initvals.h:1331:18: warning:
‘ar9580_1p0_pcie_phy_clkreq_enable_L1’ defined but not used [-Wunused-const-variable=]

drivers/net/wireless/ath/ath9k/ar9580_1p0_initvals.h:1338:18: warning:
‘ar9580_1p0_pcie_phy_clkreq_disable_L1’ defined but not used [-Wunused-const-variable=]

drivers/net/wireless/ath/ath9k/ar9580_1p0_initvals.h:1345:18: warning:
‘ar9580_1p0_pcie_phy_pll_on_clkreq’ defined but not used [-Wunused-const-variable=]

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Li Heng <liheng40@huawei.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1600831531-8573-1-git-send-email-liheng40@huawei.com