msm: smsm: Fix compile error when CONFIG_MSM_SMD isn't selected

Fix the return value of a function that currently returns NULL
(which is identified as a pointer) but is supposed to return
unsigned integer.

Change-Id: Ief97b3a1aa9640539756e88f78f6eed4e019e317
Signed-off-by: Jay Chokshi <jchokshi@codeaurora.org>
diff --git a/arch/arm/mach-msm/include/mach/msm_smsm.h b/arch/arm/mach-msm/include/mach/msm_smsm.h
index 81a6399..5173c12 100644
--- a/arch/arm/mach-msm/include/mach/msm_smsm.h
+++ b/arch/arm/mach-msm/include/mach/msm_smsm.h
@@ -353,7 +353,7 @@
 }
 static inline phys_addr_t smem_virt_to_phys(void *smem_address)
 {
-	return NULL;
+	return (phys_addr_t) NULL;
 }
 #endif
 #endif