RISC-V: Bugfix for vec_init repeating auto vectorization in RV32

RISC-V: Bugfix for vec_init repeating auto vectorization in RV32

When constructing a vector mask from individual elements we wrongly
assumed that we can broadcast BITS_PER_WORD (i.e. XLEN).  The maximum is
actually the vector element length (i.e. ELEN).  This patch fixes this.

After this patch, below failures on RV32 will be fixed.

FAIL: gcc.target/riscv/rvv/autovec/partial/multiple_rgroup_run-2.c execution test
FAIL: gcc.target/riscv/rvv/autovec/partial/multiple_rgroup_run-2.c execution test
FAIL: gcc.target/riscv/rvv/autovec/partial/multiple_rgroup_run-2.c execution test
FAIL: gcc.target/riscv/rvv/autovec/partial/multiple_rgroup_run-2.c execution test
FAIL: gcc.target/riscv/rvv/autovec/vls-vlmax/repeat_run-3.c -std=c99 -O3 -ftree-vectorize --param riscv-autovec-preference=fixed-vlmax execution test

Signed-off-by: Pan Li <pan2.li@intel.com>
gcc/ChangeLog:

	* config/riscv/riscv-v.cc (rvv_builder::get_merge_scalar_mask):
	Take elen instead of scalar BITS_PER_WORD.
	(expand_vector_init_merge_repeating_sequence): Use inner_bits_size
	instead of scaler BITS_PER_WORD.