man ECDSA_sign(3): fix wrong variable names #2

Job	Run time
compiler (gcc-7, ubuntu-20.04)	4m 31s
compiler (gcc-8, ubuntu-20.04)	4m 32s
compiler (gcc-9, ubuntu-20.04)	4m 50s
compiler (gcc-10, ubuntu-20.04)	4m 44s
compiler (gcc-11, ubuntu-22.04)	4m 44s
compiler (gcc-12, ubuntu-22.04)	5m 7s
compiler (gcc-13, ubuntu-22.04, ubuntu-toolchain-r/test)	7m 56s
compiler (clang-6.0, ubuntu-20.04)	4m 42s
compiler (clang-7, ubuntu-20.04)	4m 50s
compiler (clang-8, ubuntu-20.04)	5m 5s
compiler (clang-9, ubuntu-20.04)	5m 16s
compiler (clang-10, ubuntu-20.04)	4m 58s
compiler (clang-11, ubuntu-20.04)	4m 48s
compiler (clang-12, ubuntu-20.04)	4m 48s
compiler (clang-13, ubuntu-22.04)	5m 15s
compiler (clang-14, ubuntu-22.04)	5m 1s
compiler (clang-15, ubuntu-22.04, jammy)	5m 8s
compiler (clang-16, ubuntu-22.04, jammy)	6m 2s
compiler (clang-17, ubuntu-22.04, jammy)	5m 55s
	1h 38m 12s

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