of: Fix null pointer related warnings in base.c file
of: Fix null pointer related warnings in base.c file

Fixes the following sparse warnings:
drivers/of/base.c:176:41: warning: Using plain integer as NULL pointer
drivers/of/base.c:178:37: warning: Using plain integer as NULL pointer
drivers/of/base.c:500:49: warning: Using plain integer as NULL pointer

Signed-off-by: Sachin Kamat <1c3b1584a6008857f36c03c58f657c0fc16fc09e@linaro.org>
Signed-off-by: Rob Herring <aa00819e304141d872f2e4b1c4be422ea3abbfe1@calxeda.com>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas