RISC-V: Minor cleanup and typos when merging elf attributes.

RISC-V: Minor cleanup and typos when merging elf attributes.

	bfd/
	* elfnn-riscv.c (riscv_i_or_e_p): Minor cleanup for warnings/errors.
	(riscv_merge_std_ext): Likewise.
	(riscv_merge_arch_attr_info): Likewise.
	(riscv_merge_attributes): Likewise and fix comment typos.

	ld/
	* testsuite/ld-riscv-elf/attr-merge-priv-spec-failed-01.d: Remove
	the useless `warnings` keywords.
	* testsuite/ld-riscv-elf/attr-merge-priv-spec-failed-02.d: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-priv-spec-failed-03.d: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-priv-spec-failed-04.d: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-priv-spec-failed-05.d: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-priv-spec-failed-06.d: Likewise.