Fix a typo in fpga_reg.hpp

Author: ajaykumarkannan

sycl/include/CL/sycl/INTEL/fpga_reg.hpp

@@ -18,8 +18,8 @@ namespace INTEL {
 // This function is intended for FPGA users to instruct the compiler to insert
 // at least one register stage between the input and the return value.
 template <typename _T>
-typename std::enable_if<std::is_trivially_copyable<T>::value, T>::type
-fpga_reg(T t) {
+typename std::enable_if<std::is_trivially_copyable<_T>::value, _T>::type
+fpga_reg(_T t) {
 #if __has_builtin(__builtin_intel_fpga_reg)
   return __builtin_intel_fpga_reg(t);
 #else