build/ops: fix case-sensitive find_package call

The FindGTest.cmake module is part of the upstream cmake [1] (so it should
be the same in all distros), and it is named "FindGTest.cmake", not
"Findgtest.cmake". Fix the find_package() call introduced by
ceph#14330 so the case matches.

This fixes SUSE builds broken by that PR.

[1] https://cmake.org/cmake/help/v3.0/module/FindGTest.html

Signed-off-by: Nathan Cutler <ncutler@suse.com>

src/dmclock/CMakeLists.txt

@@ -17,7 +17,7 @@ if(K_WAY_HEAP)
 endif()
 
 if (NOT(TARGET gtest AND TARGET gtest_main))
-  find_package(gtest REQUIRED)
+  find_package(GTest REQUIRED)
   include_directories(${GTEST_INCLUDE_DIRS})
 endif()