x86/fred: Correct speculative safety in fred_extint()

In the Linux kernel, the following vulnerability has been resolved: x86/fred: Correct speculative safety in fred_extint() array_index_nospec() is no use if the result gets spilled to the stack, as it makes the believed safe-under-speculation value subject to memory predictions. For all practical purposes, this means array_index_nospec() must be used in the expression that accesses the array. As the code currently stands, it's the wrong side of irqentry_enter(), and 'index' is put into %ebp across the function call. Remove the index variable and reposition array_index_nospec(), so it's calculated immediately before the array access.