mesh: Fix coverity warning with unchecked error return
mesh: Fix coverity warning with unchecked error return

This fixes Zephyr's Coverity CID 182769.

mlaz/mynewt-core,mlaz/mynewt-core,andrzej-kaczmarek/incubator-mynewt-core,andrzej-kaczmarek/incubator-mynewt-core,andrzej-kaczmarek/apache-mynewt-core,andrzej-kaczmarek/incubator-mynewt-core,andrzej-kaczmarek/incubator-mynewt-core,andrzej-kaczmarek/apache-mynewt-core,andrzej-kaczmarek/incubator-mynewt-core,mlaz/mynewt-core,andrzej-kaczmarek/apache-mynewt-core,mlaz/mynewt-core,andrzej-kaczmarek/apache-mynewt-core,mlaz/mynewt-core