common: avb_verify: Make local data static

Fix sparse complaint:

common/avb_verify.c:14:21: warning: \
  symbol 'avb_root_pub' was not declared. Should it be static?

Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Reviewed-by: Igor Opaniuk <igor.opaniuk@linaro.org>

common/avb_verify.c

@@ -11,7 +11,7 @@
 #include <malloc.h>
 #include <part.h>
 
-const unsigned char avb_root_pub[1032] = {
+static const unsigned char avb_root_pub[1032] = {
 	0x0, 0x0, 0x10, 0x0, 0x55, 0xd9, 0x4, 0xad, 0xd8, 0x4,
 	0xaf, 0xe3, 0xd3, 0x84, 0x6c, 0x7e, 0xd, 0x89, 0x3d, 0xc2,
 	0x8c, 0xd3, 0x12, 0x55, 0xe9, 0x62, 0xc9, 0xf1, 0xf, 0x5e,