RISC-V: fix vector insn load/store width mask

RISC-V: fix vector insn load/store width mask

RVFDQ_FL_FS_WIDTH_MASK should be 3 bits [14-12], shifted down by 12 bits.
Replace GENMASK(3, 0) with GENMASK(2, 0).

Fixes: cd054837243b ("riscv: Allocate user's vector context in the first-use trap")
Signed-off-by: Jesse Taube <jesse@rivosinc.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Link: https://lore.kernel.org/r/20240606182800.415831-1-jesse@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>