[media] s5p-jpeg: get rid of some warnings

Declare this as static:

drivers/media/platform/s5p-jpeg/jpeg-core.c:732:6: warning: no previous prototype for 'exynos4_jpeg_set_huff_tbl' [-Wmissing-prototypes]
 void exynos4_jpeg_set_huff_tbl(void __iomem *base)
      ^

And don't compile this dead code, while not needed:
drivers/media/platform/s5p-jpeg/jpeg-hw-exynos3250.c:236:14: warning: no previous prototype for 'exynos3250_jpeg_get_y' [-Wmissing-prototypes]
 unsigned int exynos3250_jpeg_get_y(void __iomem *regs)
              ^
drivers/media/platform/s5p-jpeg/jpeg-hw-exynos3250.c:241:14: warning: no previous prototype for 'exynos3250_jpeg_get_x' [-Wmissing-prototypes]
 unsigned int exynos3250_jpeg_get_x(void __iomem *regs)
              ^

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>