eal/x86: fix FreeBSD build

eal/x86: fix FreeBSD build

lib/librte_eal/common/arch/x86/rte_cycles.c: In function 'rdmsr':
lib/librte_eal/common/arch/x86/rte_cycles.c:57:11:
error: unused parameter 'msr' [-Werror=unused-parameter]
 rdmsr(int msr, uint64_t *val)
           ^
lib/librte_eal/common/arch/x86/rte_cycles.c:57:26:
error: unused parameter 'val' [-Werror=unused-parameter]
 rdmsr(int msr, uint64_t *val)
                          ^
Fixes: ad3516bb4ae1 ("eal/x86: implement arch-specific TSC freq query")

Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>