mmc: dw_mmc: fix possible build error

Fix the following build errors:

drivers/mmc/host/dw_mmc-k3.c: In function ‘dw_mci_k3_suspend’:
drivers/mmc/host/dw_mmc-k3.c:58:2: error: implicit declaration of
	function ‘dw_mci_suspend’ [-Werror=implicit-function-declaration]
  ret = dw_mci_suspend(host);
  ^
drivers/mmc/host/dw_mmc-k3.c: In function ‘dw_mci_k3_resume’:
drivers/mmc/host/dw_mmc-k3.c:76:2: error: implicit declaration of
	function ‘dw_mci_resume’ [-Werror=implicit-function-declaration]
  return dw_mci_resume(host);
  ^
drivers/mmc/host/dw_mmc-k3.c: At top level:
drivers/mmc/host/dw_mmc-k3.c:53:12: warning: ‘dw_mci_k3_suspend’ defined
	but not used [-Wunused-function]
 static int dw_mci_k3_suspend(struct device *dev)
            ^
drivers/mmc/host/dw_mmc-k3.c:65:12: warning: ‘dw_mci_k3_resume’ defined
	but not used [-Wunused-function]
 static int dw_mci_k3_resume(struct device *dev)
            ^

Signed-off-by: Felipe Balbi <balbi@ti.com>
Acked-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Chris Ball <chris@printf.net>