Fix downloaded filename of snappy (#4870)

Summary:
Build failing due to incorrect filename.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4870

Differential Revision: D13637205

Pulled By: sagar0

fbshipit-source-id: 72da45d51b49bce32f696532ba0656ee0dc2b89f

Makefile

@@ -1712,7 +1712,7 @@ endif
 		echo snappy-$(SNAPPY_VER).tar.gz checksum mismatch, expected=\"$(SNAPPY_SHA256)\" actual=\"$$SNAPPY_SHA256_ACTUAL\"; \
 		exit 1; \
 	fi
-	tar xvzf $(SNAPPY_VER).tar.gz
+	tar xvzf snappy-$(SNAPPY_VER).tar.gz
 	mkdir snappy-$(SNAPPY_VER)/build
 	cd snappy-$(SNAPPY_VER)/build && CFLAGS='${EXTRA_CFLAGS}' CXXFLAGS='${EXTRA_CXXFLAGS}' LDFLAGS='${EXTRA_LDFLAGS}' cmake .. && $(MAKE) ${SNAPPY_MAKE_TARGET}
 	cp snappy-$(SNAPPY_VER)/build/libsnappy.a .