mmc: sdhci-pci: remove outdated declaration

The function was removed half a year ago, so this declaration can go,
too.

Fixes: 51ced59c ("mmc: sdhci-pci: Use ACPI DSM to get driver strength for some Intel devices")
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

include/linux/mmc/sdhci-pci-data.h

@@ -14,7 +14,4 @@ struct sdhci_pci_data {
 
 extern struct sdhci_pci_data *(*sdhci_pci_get_data)(struct pci_dev *pdev,
 				int slotno);
-
-extern int sdhci_pci_spt_drive_strength;
-
 #endif