raw/ifpga/base: fix linking with librt

raw/ifpga/base: fix linking with librt

Finding with "librt" keyword would give the output with
full path of librt such as
/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/librt.so
instead of -lrt in libdpdk.pc pkg-config file.

Assume find_library() will prepend "lib", thus remove
"lib" from "librt" keyword. The output will shows
as -lrt.

This will cause an issue when compile DPDK app with
static library as the path of librt has been hard-coded
in the libdpdk.pc file.

Fixes: e41856b515ce ("raw/ifpga/base: enhance driver reliability in multi-process")
Cc: stable@dpdk.org
Signed-off-by: Mohamad Noor Alim Hussin <mohamad.noor.alim.hussin@intel.com>
Acked-by: Tianfei Zhang <tianfei.zhang@intel.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>