RISC-V: don't recognize bogus relocations

RISC-V: don't recognize bogus relocations

With my_getSmallExpression() consistently and silently failing on
relocation operators not fitting an insn, it is no longer necessary to
hand it percent_op_itype[] "just in case" (i.e. to avoid errors when a
subsequent parsing attempt for another operand combination might
succeed). This also eliminates the latent problem of percent_op_itype[]
and percent_op_stype[] growing a non-identical set of recognized
relocation operators.