[libc][float_dec_converter_limited] Add missing LIBC_INLINE (#125655)

This caused a build failure in check-libc introduced by commit
b53da77.

Author: statham-arm

libc/src/stdio/printf_core/float_dec_converter_limited.h

@@ -112,7 +112,7 @@ struct DigitsOutput {
 // 1292913986/2^32. That is a rounded-down approximation to log10(2), accurate
 // enough that for any binary exponent in the range of float128 it will give
 // the correct value of floor(log10(2^n)).
-int estimate_log10(int exponent_of_2) {
+LIBC_INLINE int estimate_log10(int exponent_of_2) {
   return (exponent_of_2 * 1292913986LL) >> 32;
 }