kernel/riscv64: Fix cscal and zscal #5720

Job	Run time
msys2 (UCRT64, int64, Release)	17m 18s
msys2 (MINGW32, int32, Release)	17m 11s
build (ubuntu-latest, gfortran, cmake)	44m 56s
build (ubuntu-latest, gfortran, make)	22m 24s
build (ubuntu-latest, flang, cmake)	44m 4s
build (macos-latest, gfortran, cmake)	11m 45s
msys2 (CLANG64, int64, Release)	18m 56s
msys2 (CLANG64, int32, Release)	17m 17s
neoverse_build	8m 9s
build (ubuntu-latest, flang, make)	18m 14s
build (macos-latest, gfortran, make)	3m 33s
msys2 (UCRT64, int32, Release)	15m 27s
cross_build (mipsel, mipsel-linux-gnu, TARGET=MIPS1004K)	3m 18s
msys2 (UCRT64, int32, None, mingw-w64-ucrt-x86_64, fc)	14m 3s
cross_build (mips64el, mips64el-linux-gnuabi64, DYNAMIC_ARCH=1 TARGET=GENERIC)	3m 37s
cross_build (alpha, alpha-linux-gnu, TARGET=EV4)	2m 42s
cross_build (riscv64, riscv64-linux-gnu, TARGET=RISCV64_GENERIC)	2m 41s
	4h 25m 35s

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