[libc][math] Add missing parenthesis in sollya command (llvm#132298)

This PR adds the missing opening parenthesis for sollya command comment
in `libc/src/math/generic/cbrtf.cpp#L28`.

Signed-off-by: krishna2803 <[email protected]>

Author: krishna2803

libc/src/math/generic/cbrtf.cpp

@@ -25,7 +25,7 @@ constexpr double CBRT2[3] = {1.0, 0x1.428a2f98d728bp0, 0x1.965fea53d6e3dp0};
 // Degree-7 polynomials approximation of ((1 + x)^(1/3) - 1)/x for 0 <= x <= 1
 // generated by Sollya with:
 // > for i from 0 to 15 do {
-//     P = fpminimax((1 + x)^(1/3) - 1)/x, 6, [|D...|], [i/16, (i + 1)/16]);
+//     P = fpminimax(((1 + x)^(1/3) - 1)/x, 6, [|D...|], [i/16, (i + 1)/16]);
 //     print("{", coeff(P, 0), ",", coeff(P, 1), ",", coeff(P, 2), ",",
 //           coeff(P, 3), ",", coeff(P, 4), ",", coeff(P, 5), ",",
 //           coeff(P, 6), "},");