RISC-V: Fix comment/naming in attribute parsing code

RISC-V: Fix comment/naming in attribute parsing code

Function target attributes have to be separated by semi-colons.
Let's fix the comment and variable naming to better explain what
the code does.

gcc/ChangeLog:

	* config/riscv/riscv-target-attr.cc (riscv_process_target_attr):
	Fix comments and variable names.

Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>