drm/msm/dsi: fix definition of msm_dsi_pll_28nm_8960_init()

This fixes the following build failure:

drivers/gpu/drm/msm/dsi/pll/dsi_pll_28nm.o: In function `msm_dsi_pll_28nm_8960_init':
dsi_pll_28nm.c:(.text+0x1198): multiple definition of `msm_dsi_pll_28nm_8960_init'
drivers/gpu/drm/msm/dsi/pll/dsi_pll.o:dsi_pll.c:(.text+0x0): first defined here

Signed-off-by: Luis Henriques <[e-mail]>
Acked-by: Archit Taneja <[e-mail]>
Signed-off-by: Rob Clark <[e-mail]>

drivers/gpu/drm/msm/dsi/pll/dsi_pll.h

···
 struct msm_dsi_pll *msm_dsi_pll_28nm_8960_init(struct platform_device *pdev,
 					       int id);
 #else
-struct msm_dsi_pll *msm_dsi_pll_28nm_8960_init(struct platform_device *pdev,
-					       int id)
+static inline struct msm_dsi_pll *msm_dsi_pll_28nm_8960_init(
+	struct platform_device *pdev, int id)
 {
 	return ERR_PTR(-ENODEV);
 }