[media] exynos4-is: fix a format string bug

Ironically, 7d4020c3 ("[media] exynos4-is: fix some warnings when
compiling on arm64") fixed some format string bugs but introduced a
new one. buf_index is a simple int, so it should be printed with %d,
not %pad (which is correctly used for dma_addr_t).

Fixes: 7d4020c3 ("[media] exynos4-is: fix some warnings when compiling on arm64")

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>