Tegra194: sip_calls: mark unused parameter as const

This patch marks the unused parameter 'cookie', to the
plat_sip_handler() function, as const to fix an issue
flagged by the MISRA scan.

Change-Id: I53fdd2caadf43fef17fbc3a50a18bf7fdbd42d39
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>

plat/nvidia/tegra/soc/t194/plat_sip_calls.c

@@ -51,7 +51,7 @@ int plat_sip_handler(uint32_t smc_fid,
 		     uint64_t x2,
 		     uint64_t x3,
 		     uint64_t x4,
-		     void *cookie,
+		     const void *cookie,
 		     void *handle,
 		     uint64_t flags)
 {