[NFC][clang] Fix typo of riscv_rvv_vector_bits in AttrDocs (#101046)

Author: 4vtomat

clang/include/clang/Basic/AttrDocs.td

@@ -2453,7 +2453,7 @@ For example:
   typedef vint8m1_t fixed_vint8m1_t __attribute__((riscv_rvv_vector_bits(__riscv_v_fixed_vlen)));
   #endif
 
-Creates a type ``fixed_vint8m1_t_t`` that is a fixed-length variant of
+Creates a type ``fixed_vint8m1_t`` that is a fixed-length variant of
 ``vint8m1_t`` that contains exactly 512 bits. Unlike ``vint8m1_t``, this type
 can be used in globals, structs, unions, and arrays, all of which are
 unsupported for sizeless types.