kernel/riscv64:fixed the performance problem in RISCV64_ZVL256 when OPENBLAS_K is small #5713

Job	Run time
msys2 (CLANG64, int32, Release)	16m 59s
neoverse_build	7m 32s
msys2 (UCRT64, int64, Release)	15m 56s
msys2 (UCRT64, int32, Release)	15m 26s
msys2 (UCRT64, int32, None, mingw-w64-ucrt-x86_64, fc)	13m 53s
msys2 (MINGW32, int32, Release)	16m 11s
cross_build (mips64el, mips64el-linux-gnuabi64, DYNAMIC_ARCH=1 TARGET=GENERIC)	3m 47s
msys2 (CLANG64, int64, Release)	18m 38s
build (ubuntu-latest, flang, cmake)	10m 18s
build (ubuntu-latest, gfortran, cmake)	44m 54s
cross_build (alpha, alpha-linux-gnu, TARGET=EV4)	2m 42s
cross_build (mipsel, mipsel-linux-gnu, TARGET=MIPS1004K)	3m 49s
build (ubuntu-latest, gfortran, make)	21m 10s
build (ubuntu-latest, flang, make)	17m 37s
build (macos-latest, gfortran, make)	15m 11s
build (macos-latest, gfortran, cmake)	34m 47s
cross_build (riscv64, riscv64-linux-gnu, TARGET=RISCV64_GENERIC)	2m 39s
	4h 21m 29s

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