An invalid call to the CMake macro CHECK_LIBRARY_EXISTS() in
cmake/modules/FindbladeRF.cmake prevents srsLTE to enable
support for the bladeRF driver when:
* libbladeRF is installed to the same custom prefix we use to build
srsLTE, as with cmake -DCMAKE_INSTALL_PREFIX=/path/to/custom/prefix
* libbladeRF is installed to /usr/local/lib BUT the linker does not
search this path by default
This trivial patch makes FindbladeRF.cmake provide the linker with the path
libbladeRF is actually installed to.