Help the build system find system RocksDB.

Taken from this upstream commit:
https://github.com/ceph/ceph/commit/2ac26bd0e01fd6c82bd59936cf25c25173f7775a

diff --git a/cmake/modules/Findrocksdb.cmake b/cmake/modules/Findrocksdb.cmake
index f8369f73fc..5926647348 100644
--- a/cmake/modules/Findrocksdb.cmake
+++ b/cmake/modules/Findrocksdb.cmake
@@ -15,11 +15,11 @@ find_library(ROCKSDB_LIBRARIES rocksdb)
 
 if(ROCKSDB_INCLUDE_DIR AND EXISTS "${ROCKSDB_INCLUDE_DIR}/rocksdb/version.h")
   foreach(ver "MAJOR" "MINOR" "PATCH")
-    file(STRINGS "${ROCKSDB_INCLUDE_DIR}/version.h" ROCKSDB_VER_${ver}_LINE
+    file(STRINGS "${ROCKSDB_INCLUDE_DIR}/rocksdb/version.h" ROCKSDB_VER_${ver}_LINE
       REGEX "^#define[ \t]+ROCKSDB_${ver}[ \t]+[0-9]+$")
     string(REGEX REPLACE "^#define[ \t]+ROCKSDB_${ver}[ \t]+([0-9]+)$"
-      "\\1" ROCKSDB_VERSION_${ver} "${ROCKDB_VER_${ver}_LINE}")
-    unset(${ROCKDB_VER_${ver}_LINE})
+      "\\1" ROCKSDB_VERSION_${ver} "${ROCKSDB_VER_${ver}_LINE}")
+    unset(${ROCKSDB_VER_${ver}_LINE})
   endforeach()
   set(ROCKSDB_VERSION_STRING
     "${ROCKSDB_VERSION_MAJOR}.${ROCKSDB_VERSION_MINOR}.${ROCKSDB_VERSION_PATCH}")
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<div class='path'>path: <a href='/guix/log/?id=cbcc06b1d7f6cb33deb441539a67aada691aade0'>root</a>/<a href='/guix/log/tests?id=cbcc06b1d7f6cb33deb441539a67aada691aade0'>tests</a>/<a href='/guix/log/tests/import-git.scm?id=cbcc06b1d7f6cb33deb441539a67aada691aade0'>import-git.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/tests/import-git.scm?id=cbcc06b1d7f6cb33deb441539a67aada691aade0&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-09-26 17:36:59 +0200'>2023-09-26</span></td><td><a href='/guix/commit/tests/import-git.scm?id=ba21eeb565fe414b3647173068a0f3eadd174c06'>tests: Assume ‘git’ is always available.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-09-18 19:37:45 +0200'>2021-09-18</span></td><td><a href='/guix/commit/tests/import-git.scm?id=59ee10754eddddb99e4a80b9e18aa12ed1b3d77a'>import: Add 'generic-git' updater.</a><span class='msg-avail'>...</span></td><td>Xinglu Chen</td></tr>