blobfs: remove the unnecessary assert.

we will retry the alloc_cache_memory_buffer outside the function if
it fail to allocate one cache buffer.

Change-Id: I276173e449e700ceb7703f68828153f566249ae2
Signed-off-by: Cunyin Chang <cunyin.chang@intel.com>
Reviewed-on: https://review.gerrithub.io/371140
Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-by: Daniel Verkamp <daniel.verkamp@intel.com>

lib/blobfs/blobfs.c

@@ -1583,7 +1583,6 @@ alloc_cache_memory_buffer(struct spdk_file *context)
 		}
 	}
 
-	assert(false);
 	return NULL;
 }